Specimens belong to four distinctive roveacrinid types. By far the most common and largest form is represented by cups and proximal brachials with spectacular horizontal dish-like wings; on distal brachials the wings are replaced by thorns or spines. The many thousands of remains are assigned to Poecilocrinus latealatus (Figs. 4, 5, 6, 7, 8). Less common is a small species with radial extensions on the cup but lacking horizontal wings; it is assigned to Roveacrinus pyramidalis (Fig. 9). A series of most peculiar rod-shaped or stick-like brachials are assigned to this species (Figs. 10, 11). The third form is represented by large, angular cups with radial flanges, but devoid of lateral wings or processes; it is referred to Orthogonocrinus apertus (Fig. 12). A few primibrachials may belong to this species (Fig. 13). Finally, a single, small and broken cup is assigned to Roveacrinus peracutus (Fig. 12h).
Peck (1943, fig. 23) noted the following genera and species from the Duck Creek Formation: Drepanocrinus
peracutus Peck, Orthogonocrinus
apertus Peck, Roveacrinus
pyramidalis Peck, Plotocrinus
hemisphericus Peck, Pl. modulatus Peck, Pl.
inornatus Peck, Poecilocrinus porcatus Peck, Po. pendulus Peck, Po. spiculatus Peck, and Discocrinus
catastomus Peck. Thus, from this list, only Orthogonocrinus
apertus, Roveacrinus
peracutus and R. pyramidalis are represented in our material.
Poecilocrinus latealatus (Peck, 1943), Figs. 4–8.
1943 Roveacrinus latealatus Peck, Peck, p. 468; pl. 73, figs. 9–12, 14; pl. 76, fig. 1.
1943 Plotocrinus hemisphericus Peck, Peck, pl. 71, fig. 4 (first primibrachial).
1961 Poecilocrinus latealatus (Peck), Rasmussen, p. 380; pl. 55, figs. 4–5.
Cups Available cups have a wide size range, from a diameter of about half a millimetre to 3 mm. Approximately 6000 cups were examined, roughly half of them juvenile or subadult with lateral extensions or wings not yet fused into dishes. The smallest cups are low, open bowls; the aboral apex, which may be flattened, carries interradially five knobs, presumably representing vestigial basals (Fig. 4a, b). The radial articular facets slightly protrude from the upper rim so that the cups achieve a pentagonal outline at this stage (Fig. 4a, b). During growth the area below the facets is prolonged downwards and outwards developing into spoon-shaped extensions that are adorally concave (Fig. 5d–j). The outline of the extensions may vary from rounded (Figs. 4c, d; 5k, l) to spearhead shaped (Fig. 4f, h, j). During further growth the extensions increase in size until they finally merge into a wide, thin wing that is flat aborally (Fig. 4q–t) and slightly concave adorally (Fig. 6d–e). The outline of the lateral wing is mostly circular in aboral view (Fig. 4q), but may also be pentagonal (Fig. 4t). In rare cases the dish comprised more than five pieces (Fig. 4m); cups in which individual parts are lobed are somewhat more common (Fig. 4k, o). Aborally, the wings carry a medial rib or flange that extends to the apex in most cases. However, size and shape of the ribs are quite variable, especially in adult specimens. They may be curved (Fig. 4n) or branched (Fig. 4k, l). Alternatively, they may be strongly developed and thick on the aboral, globular part of the cup (Fig. 4p, q, t), they may be absent in part (Fig. 4m) of the aboral apex or altogether (Fig. 4j, l, s). In a number of specimens the aboral apex is fused with the lateral dish (Fig. 4s). In larger (adult) specimens the ribs commonly are quite thick (Fig. 4p, q, t).
Morphological changes during ontogeny are also demonstrated in lateral view (Fig. 5). The smallest cups of about half a millimetre in diameter are bowl shaped, with a flat base and radial articular facets on the upper rim (Fig. 5a, b). Growth of the processes beneath the facets starts at cup diameters approaching 1 mm (Fig. 5c, d). The downward-directed processes are first pointed (Fig. 3e–g), but then broaden and become spoon-shaped (Fig. 5h–l). However, pointed, lanceolate extensions may persist to a later stage (Fig. 5m). The spoons are supported by a rib or flange that may be quite prominent, extending beyond the aboral apex (Fig. 5p, q). At this stage the spoons are in lateral contact and eventually the lateral wings merge into a bowl that is slightly concave adorally. Cups of similar size may have widely separated (Fig. 5p) or nearly merged spoons (Fig. 5q, r; see also Fig. 4d–i). On the adoral side of post-juvenile to adult cups the radial articular facets and their interfacet processes are arranged in a ring lying on the shallow bowl of the dish formed by the lateral wings. In juvenile specimens the interfacet processes, directed upwards, are poorly developed, although present in some specimens (Fig. 5d–f). On the surface of the dish are deep clefts below the interfacet processes, but the clefts do not extend into the cavity (Fig. 6). In some specimens the interfacet processes may be of similar height (Fig. 6j), but they may also be quite variable (Fig. 6b, i).The sutures of the radials have a double ridge adorally (Figs. 5e, f, 6c, d, f, h). Broken cups commonly display a double body cavity (Fig. 6b, c, e). The upper or radial cavity is shallow and moderately wide; the lower or aboral cavity forms the globular part of the cup. A thin, mostly broken, wall may separate the two cavities (Fig. 6e), but such a wall is not present in all specimens. The radial articular facets have a deep aboral ligament pit separated from the somewhat wider axial canal by a narrow transverse ridge; the interarticular ligament fossae are indistinct, and the muscle fossae extend onto the interfacet processes (Fig. 6h–j). The variable size of the processes begs the question on muscle activity between the cup and the first primibrachials whose muscle fossae are tall and uniform (Fig. 7n–p).
Primibrachials Primibrachials number in the thousands. One specimen is preserved with cup and proximal arms still attached (Fig. 6a). The first primibrachials have a circular bowl on the aboral surface (arrows; the second primibrachial follows just above the bowl). Articulation with the second primibrachials and the following secundibrachials is not exposed because the ossicles are tightly connected, but all have an aborally concave wing. The first primibrachials have an aboral surface with a bowl proximally and an elliptical cryptosynarthry distally (Fig. 7g–s). The bowl varies from barely apparent (Fig. 7l; alternatively, this ossicle may belong to Roveacrinus
peracutus, see Fig. 13a) to large circular (Fig. 7i, m) and wide elliptical (Fig. 7o, r, s). The rim may be thickened in small bowls (Fig. 7g, h, j, k). In side view the first primibrachials are wedge shaped, with the aboral bowl conspicuously standing out (Fig. 7p). The proximal, muscular facet (Fig. 7q) matches the radial articular facet of the cup; in proximal-adoral view the facet extends into two lateral muscle fossae characterised by dense stereom (Fig. 7n–q). The second primibrachials (Fig. 7a–f) are axillary. The proximal side has a cryptosynarthrial facet, matching the distal facet of the first primibrachial. The two distal facets are muscular and are also present adorally. The body of the ossicle with the proximal and the two distal facets is on the lower side of the wing that extends laterally and distally beyond the facets; and a knob may separate the distal facets (Fig. 7a2, b, d–f). The aboral side is concave, commonly with a central rib (Fig. 7a1). Ribs may also be developed on the adoral side (Fig. 7b, d).
Secundibrachials There are many thousands of these ossicles. The arms beyond the second primibrachials do not bifurcate again. There is no indication of the presence of pinnules because corresponding sockets are lacking. In the proximal part of the crown most brachials have a wing (Fig. 8a–c, f–h, g, j–l), similar to that of the second primibrachials. The muscle facets commonly are corrugated to various degrees (Fig. 8a–d), and this is also true of brachials without wings (Fig. 8n–p, r–w). A number of brachials are connected by synostoses (Fig. 8i–o), and these occur on brachials with or without (Fig. 8i, n, o) wings. In more distal brachials the wing becomes elongate and keeled, assuming various shapes (Fig. 8p–t). Most of the distal brachials carry a conspicuous spine (Fig. 8u–w) and have only muscular facets.
Remarks Scott et al. (1977) ascribed more or less intact specimens from the Weno Formation of Fort Worth to Poecilocrinus dispandus (their reconstruction is here reproduced in Fig. 16). They are similar to the present material in certain characters, such as proximal brachials with aborally concave wings, distal brachials with spines, and the presence of synostosial arm articulations. However, specimens of P. dispandus differ in the following features. (1) The aboral part of the cup has strong ribs connected ring-like around the periphery of the apex (see Peck 1943, pl. 75, fig. 6). (2) The first primibrachial lacks a bowl or dish on the aboral surface (see Scott et al. 1977, pl. 2, fig. 4); and (3) the terminal part of the arm is pinnulate (see Scott et al. 1977, pl. 1, fig. 5). These differences suggest that the two forms do not belong to the same species. Peck (1943) described a number of species with lateral wings on the cup that he assigned to the genera Roveacrinus and Poecilocrinus. They include Poecilocrinus dispandus (with the four subspecies dispandus, explicatus, elongatus, and molestus), Po. pendulus, Po. spiculatus, Roveacrinus latealatus and R. signatus. The two last-named species were transferred by Rasmussen (1961) to Poecilocrinus. However, only Po.
pendulus and Po. spiculatus are mentioned by Peck (1943) from the Duck Creek Formation. Poecilocrinus dispandus, the type species of the genus, and its subspecies are from sites of the upper Albian Fort Worth to Main Street formations. Poecilocrinus pendulus differs from the present specimens by the downward-concave, circular wing on the radial, developed as a deep bowl (Peck 1943, pl. 75, figs. 5, 10, 13). This character is also present in Poecilocrinus spiculatus; see Peck (1943, pl. 73, fig. 6) and Rasmussen (1961, pl. 55, fig. 1a, b), who suggested that the specimens referred to this species are actually young individuals of P. pendulus. The present cups are comparable to cups of two forms described by Peck (1943). These are Roveacrinus latealatus from the Fort Worth Formation and Roveacrinus signatus which is confined to the Main Street and Grayson formations. According to Peck (1943) and Rasmussen (1961) the two species are distinguished by the development of the radial ridge or flange which leads from the aboral apex to near the edge of the wing. Rasmussen (1961, p. 380) diagnosed P. latealatus as follows: “A Poecilocrinus with a prominent, narrow, radial ridge from the dorsal point (=aboral apex) to the horizontal wing just below the articular face. The horizontal wing is very large, confluent in the interradius with the neighbouring wings around the theca (=cup), but with distinct sutures. The side-branches from the radial ridge to support the horizontal wing along the sutures are rudimentary”. Poecilocrinus
signatus was diagnosed by Rasmussen (1961, p. 381) as follows: “A Poecilocrinus with a prominent radial flange from the dorsal point to the horizontal wing just below the articular face. Side-branches from each radial flange are angularly bent and are continued in the two halves of the horizontal wing, forming together a bowl around the top of the radial ridge. The radial bowls and horizontal wings are greatly enlarged during growth, and in large specimens they are more or less confluent in the interradius”. In his discussion of P. latealatus, Peck (1943, p. 468) mentioned that, “superficially, R.
latealatus closely resembles P. dispandus…The two species cannot be differentiated from an oral view. From an aboral or side view it is evident that on R.
latealatus the main radial flange continues all the way from the aboral pole to the proximal portion of the radial facet. On representatives of P.
dispandus the flanges fork about mid-height from the calyx (=cup)”. Peck also mentioned that, “R. latealatus is probably the ancestor of R. signatus of the Main Street limestone and Grayson marl, although representatives of this line of development have not been found in the intervening formations”. Peck’s holotype of R.
latealatus (his pl. 73, fig. 14), compares well with our specimen in Fig. 4q, and Peck’s lateral view of specimen (his pl. 73, fig. 9) is comparable to Fig. 6j in the present paper. Adoral views are also similar (Peck 1943, pl. 73, fig. 12 and Fig. 6d and l here). Peck’s figures of R. signatus show specimens with forked aboral flanges (Peck 1943, pl. 74, figs. 1, 3) that are quite similar to specimens in the present material (Fig. 4k, l). In addition, Peck’s pl. 74, fig. 11 and 13 are comparable to our Fig. 4d, f, although the bowl is downward-concave in Peck’s specimens. Thus, our Duck Creek specimens have features of two of Peck’s species that are stratigraphically younger. A first primibrachial figured by Peck (1943, pl. 71, fig. 4) has an aboral bowl beneath the cryptosynarthrial facet, a distinctive character of our Duck Creek specimens. This ossicle was assigned by Peck to Plotocrinus hemisphericus, “a characteristic Duck Creek species”. Peck also figured some brachials with serrated processes comparable to some of our specimens. However, no cup assignable to P. hemisphericus is in the present material. The morphological changes during development as well as the large variation in adult specimens prevent classification into more than one species. Because the majority of cups in our material are closer to the holotype of P. latealatus than to that of Poecilocrinus signatus I assign them to the former. The Duck Creek specimens with forked ribs (Fig. 4k, l, n) suggest a line of development leading to P. signatus. Such development was already suggested by Peck (1943, figs. 1–22).
The genus Poecilocrinus was established by Peck (1943, p. 471) with the following diagnosis: “Roveacrininae in which the radial ornamentation consists of a single flange that bifurcates at mid-height or below, each branch connecting with the outside proximal portion of the arm facet to form an enclosed, more or less circular depression under the arm facet, the depression on most specimens remaining hollow but being occasionally bisected by a vertical flange of secondary origin”. This diagnosis is difficult to follow and was modified by Rasmussen (1961, p. 378) to read, “Roveacrinidae in which the theca (=cup) is provided with a prominent, horizontal wing on each radial, sometimes fused around the theca, or each radial has a curved, bowl-shaped wing with the opening of the concavity outward or downward. There is a radial ridge from the wings to the dorsal point (=aboral apex). The articular facets are fairly large, outward-sloping, and connected with the wings by short lateral ridges. The interfacet processes are rather short and stout. The radial cavity is large.” This diagnosis, adopted in the Revised Treatise (Hess and Messing 2011), may be enlarged as follows: “Proximal brachials with aborally concave wing, distal secundibrachials with spine; corrugated adoral processes common, a number of secundibrachials articulated by flat synostosis.”
Roveacrinus pyramidalis
Peck, 1943, Figs. 9–11.
1943 Roveacrinus pyramidalis Peck, Peck, p. 468; pl. 72, figs. 24–29.
1943 isolated brachials of unknown affinities, Peck, p. 473; pl. 76, figs. 23, 27, 42, 44.
?1943 Plotocrinus primitivus Peck, Peck, p. 470; pl. 71, figs. 1–3.
1961 Roveacrinus pyramidalis Peck, Rasmussen, p. 371; pl. 53, figs. 10–11.
1961 brachials of Roveacrinidae, Rasmussen, pl. 56, figs. 9–11.
Cups (Fig. 9) The material contains 375 cups. The diameter ranges from about 0.5 to 1 mm. The outline is roughly pentagonal, and the profile more or less pyramidal. Some small cups are broken above the aboral apex, exposing a lower chamber with spherical bodies, presumably basals (Fig. 9a–d). The surface is coarsely reticulate. The articular facets are roughly triangular and prolonged downwards into prominent processes of irregular shape, giving the cups a ragged appearance. The processes also occur in smaller individuals where they are produced into spines (Fig. 9b–e); these may not be developed on all sides. The articular facets have a deep aboral ligament pit separated from the small central canal by a narrow transverse ridge. The interarticular ligament fossae are indistinct, and the muscle fossae extend onto interfacet processes of variable height; some cups may have processes of different height (Fig. 9h, k).
Primibrachials (Fig. 10) The material includes a significant number (373, many of them broken) of tall second primibrachials that were attached by a sloping cryptosynarthrial facet to the smaller first primibrachials (Fig. 10d, q). There are only 17 first primibrachials that can be combined with the axillaries. They have a roughly triangular proximal muscular facet (Fig. 10n, o) matching the facet of the cups (Fig. 10r). The muscle fossae are prolonged adorally, matching the corresponding processes on the cup (Fig. 10o, arrow). Their proximal part is slightly thickened and has a reticulate structure comparable to that of the cup (Fig. 10k, l, q). The shaft is smooth and composed of dense stereom. A series of small pits may be developed along the adoral–aboral margin (Fig. 10o). The distal facet, seen aborally, is a strongly sloping cryptosynarthry of somewhat variable height. However, most of the available ossicles have a facet that is lower than the proximal facet of the following second primibrachial. These axillary ossicles are unusually tall. The proximal facet is cryptosynarthrial and strongly sloping. The facet may sit on a pedestal (Fig. 10d) but mostly reaches the lower (proximal) end (Fig. 10e, g–i). In large ossicles this part resembles the sole of a shoe in side view (Fig. 10i). In section, the second primibrachials are elliptical to laterally compressed; exceptionally, they are adorally keeled (Fig. 10f). The shaft commonly bears a row of shallow pits on the adoral side (Fig. 10e, g, h); occasionally there is a narrow, weak continuous furrow. At the distal end are two muscular facets for articulation with the first secundibrachials (Fig. 10b, c, f, h, i), they are directed outwards (aborally) at an angle of about 60°; exceptionally there is only one facet so that the arm did not branch in this case (Fig. 10a). The facets have a strong relief, with pronounced aboral ligament fossa and axial canal, flanked by similarly produced interarticular ligament fossae; the muscle fossae extend onto narrow processes. Such articulation suggests considerable power for arm movement at this place.
Secundibrachials (Fig. 11) The secundibrachials number in the thousands. They vary greatly in shape (Fig. 11), and many cannot be assigned to a definite position in the crown. Similar to the primibrachials, none has a distinct food groove. No further axillary brachials have been found so that the arms must have branched only at the second primibrachials. Brachials illustrated in Fig. 11m–p appear to be first secundibrachials. The proximal facet is muscular, the distal synostosial and outward-sloping. The aboral side of the shaft has a median ridge and lateral flanges. The ossicles vary in height. First secundibrachials of similar shape were figured by Rasmussen (1961; pl. 56, fig. 3) in a cup of R. peracutus, from the Cenomanian of Cambridge, with attached primibrachials. The second primibrachials (primaxils) of this specimen are also high and slender, but they differ from the present material by a narrow median ridge and thin lateral flanges. Some brachials (Fig. 11h–i) are laterally compressed, similar to Fig. 11p; yet distally they have muscular facets with long processes for muscle fossae. Other brachials (Fig. 11d–e) have muscular facets at both ends matching the distal facets of the second primibrachials (Fig. 10a–c). However, they cannot be first secundibrachials because the distal facet is also muscular, not synostosial. Second secundibrachials with proximal synostosial facet and distal muscular facet have not been found. A number of brachials appear to have a pinnule socket (Fig. 11f, i), although in other brachials of similar morphology such a structure is weak (Fig. 11h). A single brachial carries a worm-like process, perhaps an epizoan (Fig. 11g). The material includes quite a number of tall brachials with an aboral keel and muscular facets at both ends (Fig. 11j–l), they are presumably from median arm portions. Somewhat smaller brachials are strongly compressed laterally and, except for a keel, almost transparent (not figured). The smallest brachials from distal parts of the arms are common. They have muscular articulations at both ends and adoral processes for muscle attachment (Fig. 11a–c). As in the other secundibrachials distinct food grooves along the body are lacking, but small impressions similar to the axillary primibrachials (Fig. 10g–h) may be seen on the adoral side (Fig. 11c).
Remarks Peck (1943, pl. 76) figured a number of brachials from the Duck Creek Formation which he could not assign to any given species. In this he was followed by Rasmussen (1961; pl. 56, figs. 9–11) who did not discuss either the particularly tall, rod-shaped second primibrachials or their possible function. Similar brachials with a height of 1 mm or so, including axils, were figured by Kristan-Tollmann (1970, fig. 5) from the Cassian Formation (upper Ladinian/Carnian) of the Dolomites (see also Hess in Hess and Messing 2011). She assigned these remains to the somphocrinid Osteocrinus rectus
rectus (Frizzell & Exline 1955). As in the present material the Triassic form has brachials articulated by both muscular and cryptosynarthrial facets. Food grooves (“Ventralfurchen”) may extend all along the ossicle, or they may be developed only near muscular articulations; alternatively, they may be dissolved into small pits or be absent altogether. In the present material, proper food grooves are either lacking or are dissolved into a series of small pits on the adoral side with its cryptosynarthrial facet (Fig. 10e, g, h). The axillary facets for the secundibrachials are directed outwards (aborally). The combination of the peculiar tall axils with the cups of R.
pyramidalis is supported by matching facets between the different elements (cup and primibrachials); one cup has a first primibrachial attached, but displaced into the cavity. The cups are coarsely reticulate, with irregular vertical flanges or processes beneath the facets. The primibrachials are connected by a sloping cryptosynarthry. It may be particularly tall in the second primibrachials (Fig. 10g–i). Such ossicles match only with part of the corresponding facet of the mostly small first primibrachials. However, there are pairs that match well (Fig. 10q, e), even in cases where the second primibrachial is much larger (Fig. 10q, d). Some of the axils have a downward prolongation of the shaft beyond the facet (Fig. 10d). The position of the axial canal near the upper end of tall facets may indicate that articulation with the first primibrachial was restricted to the upper part (Fig. 10g); such an assumption is supported by a slight angle of the facet in the large ossicle in Fig. 10i, with the upper third serving for articulation.
Orthogonocrinus apertus
Peck, 1943, Figs. 12–13.
1943 Orthogonocrinus apertus Peck, Peck, p. 464; pl. 76, figs. 2–8.
1955 Orthogonocrinus apertus Peck, Peck, p. 1022; pl. 106, figs. 7–9.
1961 Orthogonocrinus apertus Peck, Rasmussen, p. 385; pl. 56, figs. 4–5.
Cups (Fig. 12) The 240 cups correspond well to the material described by Peck (1943). The size of the cups ranges from less than 1 mm in height to about 3 mm. The smallest cup (Fig. 12g) has convex radials with only a faint aboral ridge; it is open at the lower end where the unbroken radials suggest that a ring of basals was originally present. Adult cups are more or less conical. Each radial has a vertical ridge extending from the facet to the aboral apex and beyond, as demonstrated by one of Peck’s specimens (1943, pl. 76, fig. 3). However, most of the cups are broken in the lower part exposing an aboral cavity that is of much greater height than the upper one. The cavities are separated by a horizontal partition (Fig. 12d). The partition has five peripheral and a central opening connecting the two chambers (Fig. 12e). The articular facets are angularly bent at the transverse ridge. The aboral ligament fossa is vertical and prominent on the side of the cup; it has a deep pit below the transverse ridge. The interarticular ligament fossae and the axial canal are situated on the upper, nearly horizontal or slightly inclined part of the facet. The interfacet processes are of unequal height and shape, even in a single individual. The muscle fossae extend to the lower part of the processes; they are separated from the radial cavity by a thin wall forming a V-shaped notch (Fig. 12j). In adoral view the interfacet processes project into the radial cavity, giving the cup a characteristic appearance (Fig. 12b).
Primibrachials (Fig. 13) There is a limited number of wingless primibrachials that may belong to this species. Some of the first primibrachials have corrugated muscle facets on the adoral side and are somewhat crooked (Fig. 13b, c, e). The aboral side lacks a bowl as developed in Poecilocrinus latealatus. The asymmetric profile may be the result of unequal interfacet processes to the base of which the muscles attached. Second primibrachials are aborally concave and smooth. The proximal facet is a cryptosynarthry matching the distal facet of the first primibrachial; the two distal facets are muscular and separated by a process.
Remarks Most of the cups of this distinct species are broken at the lower (distal) end, exposing the aboral cavity (hence the species name). However, the cups probably were closed at the bottom during life, as demonstrated by practically intact specimens (e.g. Peck 1943, pl. 76, fig. 3). In the present material, the specimen in Fig. 12f is largely intact. It seems possible that the smallest individuals originally were closed at the apex by a basal circlet that was later resorbed (Fig. 12g). In any case, the lower part of the cups of this species is prone to breakage as a result of the thin wall (Fig. 12e). Rasmussen (1961, p. 386) mentioned second primibrachials with broad lateral wings found together with cups of the present species. These remains are from the Santonian of Corneville (France) and are housed at the Geneva Museum. They are closely similar to those of Roveacrinus
communis
Douglas
1908 from the upper Cenomanian of Germany as figured by Rasmussen (1961, pl. 53, figs. 4 and 6); in this specimen the first primibrachials are covered by the second ones. The first primibrachials tentatively assigned to the present species lack distinct lateral wings or aboral bowls.
Roveacrinus
peracutus (Peck
1943), Figs. 12h, ?13a, d.
1943 Drepanocrinus peracutus Peck, Peck, p. 463; pl. 76, figs. 9–22, 26, 28.
1943 isolated brachials of unknown affinities, Peck, p. 473; pl. 76, figs. 30, 33–35.
1955 Styracocrinus peracutus (Peck), Peck, p. 1022; pl. 106, figs. 10–12.
1955 unidentified primaxils, Peck, p. 1025; pl. 106, figs. 14–15.
1961 Styracocrinus peracutus (Peck), Rasmussen, p. 383; pl. 56, figs. 1–3.
1983 Styracocrinus peracutus (Peck), Pisera, p. 387; pl. 11, figs. 1–8; pl. 12, figs. 1–6.
The cup assigned to this species is small and broken below the facets. These are rather indistinct, only slightly angularly bent at the transverse ridge and prolonged downwards into flanges. The greatest diameter of the cup is just below the facets where the flanges are accompanied by lateral depressions. The interfacet processes are low. From below the aboral cavity has a partition with a distinct central opening but only small peripheral openings (see Fig. 17e for a specimen from Del Rio). First primibrachials with straight, non-corrugated adoral sides may belong to the present species (Fig. 13a, d), although the specimen in Fig. 13a may also belong to Poecilocrinus latealatus where much reduced bowls rarely occur (the specimen is also illustrated in Fig. 7l).
Remarks This cup is distinguished from Orthogonocrinus apertus by its articular facets which narrow aborally into radial flanges. It corresponds to the material described by Peck (1943) as Drepanocrinus
peracutus, a species later transferred by the same author (Peck 1955) to Styracocrinus. This genus is here considered a synonym of Roveacrinus (see below).
