EOCENE ECHINODERMATA. 141 



The peristome is excentric anteriorly, immediately beneath the apical system, pentagonal, 

 longitudinally elongate, with a floscelle. 



The periproct is elliptical, transverse, supramarginal, located in a rather deep, oval indenta- 

 tion at the top of the slight posterior truncation. The edges of the indentation are almost even 

 with the posterior margin. Below the periproct a vaguely denned, broad, shallow groove extends 

 downward across the margin. 



Related forms. — Cassidulus holmesi is not closely allied to any American form. Its broadly 

 oval and uniformly convex form, nearly equal ambulacral petals, and the details of its periproct 

 and peristome readdy distinguish it. It does not appear to be closely related to any foreign 

 form. 



Locality. — Santee Kiver (?), S. C. 



Geologic horizon. — Probably in the McBean formation of Claiborne group, middle Eocene. 

 The matrix is a fine-grained greensand such as is known to occur on Santee Kiver. 



Collection. — American Museum of Natural History. 



Cassidulus (Rhynchopygus) lyelli (Conrad). 

 Plate LXV, figures 4a-d. 



Nucleolites lyelli Conrad, 1850, Acad. Nat. Sci. Philadelphia Jour., 2d ser., vol. 2, p. 40, fig. 14. 



Cassidulus lyelli Conrad, 1865, Acad. Nat. Sci. Philadelphia Proa, p. 75. 



Pygorhynchus lyelli Cotteau, 1888, Paleontologie francaise, Echinides eocenes, vol. 1, p. 550. 



Nucleolites lyelli Boyle, 1893, U. S. Geol. Survey Bull. 102, p. 200. 



Pygorhynchus lyelli Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 696. 



Determinative characters. — Test low, oval in marginal outline, truncated at the posterior end; 

 upper surface convex, depressed; under surface slightly concave around the peristome; apex 

 slightly excentric posteriorly. Ambulacral areas narrow, dorsal portions petaloid; petals long, 

 elliptical. Poriferous zones narrow; pores subequal; interporiferous areas rather wide. Apical 

 system excentric anteriorly. Peristome excentric anteriorly, beneath the apical system, sub- 

 pentagonal to subtriangular, with a floscelle. Periproct suboblong to dumbbell shaped, trans- 

 versely elongate, supramarginal, nearly flush with the truncated posterior face of the test; with 

 an overhanging rostrum. 



Dimensions. — Length 33 millimeters; width 28 millimeters; height 15 millimeters. 



Description. — The present whereabouts of the type of Conrad's Cassidulus lyelli is unknown; 

 but as the present species answers so well to Conrad's description and drawings and as it came 

 from about the same locality, it is thought highly probable that it is the same. However, as 

 only a single somewhat imperfect specimen is known, further collecting may show that it is not 

 Conrad's form, in which case the present species will have to receive a new name. The test is 

 regularly oval or subelliptical in marginal outline, vertically truncated at the posterior end. The 

 upper surface is low, almost uniformly convex, depressed, slightly more elevated posteriorly 

 than anteriorly; under surface slightly convex posteriorly, faintly concave around the peristome. 

 The apex is slightly excentric posteriorly. 



The ambulacral areas are narrow, dorsal portions petaloid, petals long, symmetrically 

 elliptical, somewhat open at the ends, the posterior pair longer than the others, which are nearly 

 equal in length. The poriferous zones are narrow, similar; pores subequal in size, outer row 

 oval, inner row round, pairs of pores conjugate; interporiferous areas relatively rather wide. 



The surface of the test is closely set with small scrobiculate tubercles, which are larger on 

 the under surface. The under surface is poorly preserved on the single specimen obtained; 

 but there appears to have been a median band back of the peristome which was somewhat 

 smoother than the adjacent areas and was more or less pitted. 



The apical system is excentric anteriorly, being about three-eighths the length of the test 

 from the anterior end. The details can not be made out, beyond the fact that there are four 

 genital pores of which the anterior pair are nearer together than the posterior. 



The peristome is excentric anteriorly, immediately beneath the apical system. It is 

 poorly preserved; but there is enough to show that it is subpentagonal, though approaching a 

 subtriangular form, and surrounded by a somewhat inconspicuous floscelle. 

 39800°— 15 10 



