142 MESOZOIC AND CENOZOIC ECHINODEBMATA OF THE UNITED STATES. 



The periproct is subelliptical to suboblong, considerably elongated transversely, supra- 

 marginal, at the top of and nearly flush with the vertically truncated posterior surface of the 

 test. The rounded central part of the upper edge extends downward so as to break the ellipti- 

 cal contour of the periproct, and projects slightly beyond the periproct so as to slightly overhang 

 the vaguely defined broad and shallow groove which extends below the periproct across the 

 posterior margin. 



Related forms. — Cassidulus lyelli is quite distinct from all other representatives of the 

 genus from American strata. Its transversely suboblong periproct and its low regularly oval 

 form readily permit of its identification. It does not appear to be closely related to any foreign 

 form. 



Locality. — In Baker County, Ga. 



Geologic horizon. — Jackson formation, upper Eocene. 



Collection. — Boston Society of Natural History (1552a). 



Cassidulus (Rhynchopygus) raveneli Twitchell, n. sp. 

 Plate LXV, figures oa-d; Plate LXVI, figures la-c, 2a-b. 



Pygorhynchus crucifer Ravenel, 1848, EchinidBe, recent and fossil, of South Carolina, p. 4, PI. II, figs. 9, 10. 

 Pygorhynchus crucifer Bavenel, 1850, Cat. recent and fossil Eehinidse of South Carolina: Am. Assoc. Adv. Sci. Proa, 



vol. 3, p. 160. 

 Ravenelia crucifer McCrady, 1859, Elliott Soc. Nat. Hist. Charleston Proc, vol. 1, pp. 282, 283, no figure. 

 Pygorhynchus crucifer Agassiz, 1883. Mus. Comp. Zool. Mem., vol. 10, No. 1, p. 91. 

 non Nucleolites crucifer Morton, 1834, Synopsis organic remains Cretaceous, p. 75, PI. Ill, fig. 15. 

 non Trematopygus crucifer Clark, 1891, Johns Hopkins Univ. Circ, vol. 10, No. 87, p. 76. 

 non Trematopygus crucifer Clark, 1893, U. S. Geol. Survey Bull. 97, p. 63. 



Determinative characters. — Test hemielhpsoidal, elliptical in marginal outline, truncated 

 at posterior end; upper surface considerably depressed, convex, declining more gently to the 

 ends than to the sides; under surface slightly concave longitudinally. Ambulacra petaloid, 

 the posterior petals longer than the others and bending outward toward their ends. On the 

 under side there is a wide, longitudinal, median band, where the tubercles are replaced by a 

 more or less pitted surface. Apex central; apical system excentric anteriorly. Peristome 

 pentagonal, excentric anteriorly, with a well-defined floscelle. Periproct supramarginal, 

 rather large, elliptical, transverse, concealed beneath an overhanging rostrum at the head of a 

 short, broad sulcus. 



Dimensions.; — Specimen A (type): Length 40 millimeters; width 29 millimeters; height 14 

 millimeters. Specimen C: Length 55 millimeters. Largest specimen seen: Length 55 milli- 

 meters; width 39 millimeters; height 18 miUimeters. 



Description. — Dr. Edmund Ravenel, of Grove, S. G, in 1848, in a pamphlet of which 

 but a few copies were printed, 1 gave some good figures of a form which is evidently the same 

 as the one here described. He gave no description and did not regard the form as new; but 

 said it was the same as Nucleolites crucifer Morton and placed it in the genus Pygorhynchus. 

 Ravenel was undoubtedly mistaken in regarding his form as the same as that of Morton, for 

 there is hardly more than a superficial resemblance between them. W. B. Clark assigns Morton's 

 form to the genus Trematopygus, whereas the form which Ravenel figured and which is here 

 described for the first time is a Cassidulus of the Rhynchopygus type. However, in view of 

 Ravenel having been the discoverer of the form and in recognition of his interest in and additions 

 to the knowledge of the fossil Echinoidea of South Carolina this interesting species is named 

 after him. 



The test of tins species is hemielhpsoidal in form, regularly elliptical in marginal outline, 

 and truncated and slightly indented at the posterior end. The upper surface is low, depressed, 

 and rather uniformly convex, though more abruptly so transversely than longitudinally; under 

 surface slightly concave along the longitudinal median area, the concave portion being limited 

 along the sides by the somewhat inferiorly projecting side edges. The apex is central. 



i The Library of Congress at Washington possesses the copy which was studied by the writer. 



