492
Journal of Paleontology 92(3):488–505
Diagnosis.—Reteocrinids with bilateral symmetry through A ray and CD interray; interrays depressed, not ankylosed, com- prised of numerous small, irregularly arranged plates; median ray ridges prominent; infrabasals upright, visible in side view; depressions between basal plates and variably between infra- basal plates, in some cases filled with small irregular plates; posterior interray wide with prominent anitaxial ridge originat- ing from CD basal; first arm branching varies in position from radial plate to sixth primibrachial; fixed brachials bifurcating several times within the calyx; free arms uniserial, apinnulate, branched; stem circular, pentagonal, or pentalobate, commonly pentameric in dististele.
Occurrence.—Upper Ordovician (Sandbian–Katian); United States (Oklahoma, Tennessee, Ohio, Illinois) and Canada (Ontario).
Remarks.—Species-level characters in Reteocrinus include shape of the calyx, plate ornamentation, condition of the inter- infrabasal areas, shape of the infrabasals, number of primibra- chials, and stem characteristics (Kolata, 1982; Guensburg, 1984). One of the defining characteristics of species of Reteocrinus is the presence of spaces between basal plates (interbasal gaps) and indentations between infrabasal plates (interinfrabasal depres- sions). The suturing of cup plates around these spaces gives the cup a reticulated appearance. In some species (e.g., R. stellaris), the interbasal gaps are filled with small plates.
Reteocrinus stellaris Billings, 1859 Figure 3.9, 3.10
Holotype.—GSC 1525 (lectotype).
1859 Reteocrinus stellaris Billings, p. 64, pl. 9, figs. 4a–e. 1868 Reteocrinus stellaris; Shumard, p. 394. 1868 Retiocrinus stellaris [sic]; Bigsby, p. 23.
1889 Reteocrinus stellaris; Miller, p. 277, fig. 416. 1897 Reteocrinus stellaris; Wachsmuth and Springer, p. 178, pl. 9, figs. 3a–c.
1883a Reteocrinus stellaris; Wachsmuth and Springer, p. 261, figs. 1–3.
1910 Reteocrinus stellaris; Grabau and Shimer, p. 547. 1911 Reteocrinus stellaris; Springer, p. 10, pl. 1, figs. 6, 7. 1915 Reteocrinus stellaris; Bassler, p. 1100. 1938 Reteocrinus stellaris; Bassler, p. 163. 1943 Reteocrinus stellaris; Bassler and Moodey, p. 660. 1946 Reteocrinus stellaris; Wilson, p. 25. 1973 Reteocrinus stellaris; Webster, p. 230. 1978b Reteocrinus stellaris; Ubaghs in Moore and Teichert, p. T414, figs. 223.1a, b.
1984 Reteocrinus stellaris; Guensburg, p. 28, pl. 4, figs. 1–3. 1985 Reteocrinus stellaris; Smith, p. 168, pl. 7.4.10.
1986 Reteocrinus stellaris; Webster, p. 274. 1988 Reteocrinus stellaris; Webster, p. 145.
Diagnosis.—Reteocrinus with three primibrachials; radials, basals, and infrabasals ornamented with angular keeled ridges that surround interbasal depressions; fixed brachials lacking lateral projections; interbasal depressions filled with small, irregular plates; interinfrabasal depressions shallow or indis- tinct; stem circular.
Occurrence.—Previously, R. stellaris had been reported from Upper Ordovician (Katian) occurrences from the Hull and Cobourg formations, Ottawa Group, Ontario. The occurrence reported here is from the Bobcaygeon–Verulam contact zone, Carden Quarry, Upper Ordovician (lower Katian).
Materials.—UMMP 74671 (Bobcaygeon–Verulam contact zone, Carden Quarry).
Remarks.—Thorough description of R. stellaris is provided in Guensburg (1984), so a redescription is not necessary. Relative to R. alveolatus, R. stellaris is uncommon in the collection described here from the Brechin region. Unlike R. alveolatus, specimens of this species display small, polygonal plates filling the interbasal gaps (Fig. 3.10)
Reteocrinus alveolatus (Miller and Gurley, 1894) Figure 3.1–3.8
Holotype.—FMNH 6045.
1894 Retiocrinus alveolatus Miller and Gurley [sic], p. 26, pl. 2, fig. 22.
1897 Retiocrinus alveolatus [sic]; Miller, p. 752, fig. 1390. 1911 Reteocrinus alveolatus; Springer, p. 10, pl. 1, figs. 1–5. 1915 Reteocrinus alveolatus; Bassler, p. 1100. 1943 Reteocrinus alveolatus; Bassler and Moodey, p. 659. 1978b Reteocrinus alveolatus; Ubaghs in Moore and Teichert, p. T414, fig. 223.1c, d.
1984 Reteocrinus alveolatus; Guensburg, p. 29, pl. 4, figs. 5–7, 9, 14, 15.
Diagnosis.—Reteocrinus with two to four primibrachials; cup plates with rounded keeled ridges; cup plates and fixed brachials smooth or ornamented with faint, irregular, discontinuous ridges; fixed brachials with spine-like processes projecting laterally into interradial areas; interinfrabasal gaps deep, small, diamond-shaped to semicircular; interbasal gaps deep, filled with small, irregular plates; stem pentagonal to pentastellate, distally pentameric.
Figure 3. Reteocrinus specimens from the Bobcaygeon-Verulam contact zone, southern Ontario. (1–3) Reteocrinus alveolatus UMMP 74675, (Carden Quarry), distal crown showing terminus of anal tube above arms; (1) lateral view of crown; (2) lateral view of crown, opposite side; (3) adoral view of anal tube and terminal arm tips; (4–6) Reteocrinus alveolatus UMMP 74673 (LaFarge Quarry); (4) lateral view of complete specimen with stem and holdfast; (5) lateral view of crown; (6) close-up of holdfasts attached to hardground surface; (7) Reteocrinus alveolatus UMMP 74674 (Carden Quarry); (8) Reteocrinus alveolatus UMMP 74672 (LaFarge Quarry); (9, 10) Reteocrinus stellaris, UMMP 74671 (Carden Quarry); (9) lateral view of crown and proximal stem; (10) close-up of calyx showing interbasal gap plates, photographed under alcohol. All scale bars 5mm.
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