1010
Journal of Paleontology 91(5):1001–1024
Peristome large, ~60% of diameter, slight buccal notches, well- developed tags, single perradial sphaeridial pit.
Occurrence.—Clayton Formation, 0.25 mile east of State Highway 25 between MLK Dr. and Pollard Rd., west side of Starkville, Oktibbeha County, Mississippi (UTM Zone 16, E 328,035 m, N 3,702,780 m, NAD83).
Figure 6. Micropsidia salis (Cooke, 1941), MMNS 5304.1 from the Clayton Formation, Palmyra tract, Lowndes County, AL. Detail of apical disc showing insert ocular I, with annotation following the plate-naming convention of Lovén (1874). Scale bar 2mm.
material in the size of secondary tubercles, which are larger in the Vincentown specimens.
Order Arbacioida Gregory, 1900 Family Arbaciidae Gray, 1855 Genus Arbaciella Mortensen, 1910
Arbaciella? sp. Figure 5.8–5.10
Material.—MMNS 7814, from the Clayton Formation, Starkville, Oktibbeha County, Mississippi.
Diagnosis.—Imperforate, non-crenulate tubercles below the ambitus, peg-like pustules above, with vertical epistromal ridges linking larger pustules. Slight buccal notches, well-developed tags, single perradial sphaeridial pit.
Description.—Small. Primary tubercles imperforate and non- crenulate, one to each ambulacral plate, two to each inter- ambulacral plate, restricted to area below ambitus; smaller, peg-like pustules aborally, in oblique linear sets, usually one per ambulacral plate, three per interambulacral plate, vertical epis- tromal ridges link larger pustules. Ambulacra trigeminate, apparently throughout (but preservation obscures some of the ambulacra), pores equal sized, arbacioid compounding.
Remarks.—Asingle specimenwith broken and incomplete aboral surface was found just above the paraconformity between the Upper Cretaceous Prairie Bluff Chalk and the Paleocene Clayton Formation. The incompleteness of the specimen, in particular the complete lack of genital plates, precludes a complete description of the species and definitive generic assignment. It is left in open nomenclature pending discovery of additional material. Because of the overlap of the interambulacral tags, a primibasal plate is not discernible, nor is a single primary tubercle, evidence that this is not a species of the closely related genus
Podocidaris.Additionally, there is uncertainty as to the validity of the genus Arbaciella itself (Kroh et al., 2012), further justifying the indefinite generic assignment of this species.
Order Cassiduloida Agassiz and Desor, 1847 Family Pygaulidae Lambert, 1905 Genus Plagiochasma Pomel, 1883
Plagiochasma cruciferum (Morton, 1830a) Figures 7.1, 7.2, 8.1–8.5
1830a Ananchytes cruciferus Morton, p. 245, pl. 3, fig. 8. 1830b Ananchytes cruciferus; Morton, p. 201. 1833 Nucleolites crucifer; Morton, p. 294. 1834 Nucleolites crucifer; Morton, p. 75, pl. 3, fig. 15. 1840 Nucleolites crucifer; Agassiz, p. 4. 1847 Nuculites cruciferus; Agassiz and Desor, p. 155. 1850 Nucleolites cruciferus;d’Orbigny, p. 271. 1850 Pygorhynchus crucifer; Ravenel, p. 160. 1854 Echinobrissus crucifer;d’Orbigny, p. 25. 1853– Trematopygus crucifer;d’Orbigny, p. 387, pl. 953, 1856 figs. 10–11; pl. 963, figs. 1–5. 1858 Nucleolites (Trematopygus) crucifer; Desor, p. 262. 1891 Trematopygus crucifer; Clark, p. 76. 1893 Trematopygus crucifer; Clark, p. 63, pl. 27, figs. 1a–i. 1907 Trematopygus crucifer;Weller, p. 289, pl. 11, figs. 1–9. 1915 Trematopygus cruciferus; Clark in Clark and Twitchell, p. 71, pl. 28, figs. 3a–c; pl. 29, figs. 1a–f.
1942 Trematopygus crucifer; Cooke, p. 10. 1959 Rhopostoma cruciferum; Cooke, p. 26, pl. 7, figs. 1–4.
1977 Rhopostoma cruciferum; Toulmin, p. 179, pl. 9, figs. 10–13.
1982 Rhopostoma cruciferum; Rose, p. 149. 2000 Plagiochasma cruciferum; Jagt, p. 252, pl. 17, figs. 4–6.
Figure 7. Plagiochasma cruciferum (Morton, 1830) from the Clayton Formation, Cedar Creek, Butler County, AL: (1) MMNS 7173.1, aboral; (2) MMNS 7173.1, oral. Gitolampas georgiensis (Twitchell, 1915) from the Clayton Formation, Palmyra tract, Lowndes County, AL: (3) MMNS 5299.1, aboral; (4) MMNS 5299.1, oral; (5) MMNS 5299.2, detail of apical disc; (6) MMNS 5299.1, posterior. Pseudholaster cinctus (Morton, 1830) from the Vincentown Formation, Big Brook, Marlboro, Monmouth County, New Jersey: (7) USNM 540912, aboral; (8) USNM 540912, oral. Echinocorys ovalis (Clark, 1893) from the Vincentown Formation, Vincentown, Burlington County, NJ: (9) USNM 636366, lectotype, aboral; (10) USNM 636366, lectotype, oral. Scale bars are (1, 2, 6) 10mm; (5) 2mm; (3, 4, 7–10) 20mm.
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