146 MESOZOIC AND CENOZOIC ECHINODEKMATA OF THE UNITED STATES. 



The ambulacral areas are narrow, dorsal portions petaloid; petals long, narrow, and open 

 at their ends, the posterior pair being longer than the others which arc nearly equal in length. 

 The poriferous zones are narrow, the adjacent zones of the anterior and posterior paired petals 

 being slightly broader and straighter than the others; pores small, outer row slitlike, inner 

 row round, pairs of pores conjugate. 



The apical system is very excentric anteriorly, being located less than a third of the length 

 of the test from the anterior end. There are four genital pores, of which the anterior pah- 

 are nearer together than the posterior; and there are five small perforated radial plates. These 

 are the only details that can be made out on the specimens. 



The surface of the test is closely set with very small imperforate tubercles with deep 

 scrobicules. The tubercles are slightly larger on the under surface except along a narrow 

 median band back of the peristome, which is free from tubercles, nearly smooth and dotted with 

 numerous very small pits. 



The peristome is excentric anteriorly, less so than the apical system, pentagonal, trans- 

 versely elongate, with a well-defined floscelle. 



The periproct is rather large, elliptical, transverse, supramarginal, at the top of the pos- 

 terior truncation; beneath a rounded, transverse, somewhat protruding expansion of the test 

 whose edge is about even with the truncated posterior margin. 



Related forms.' — Cassidulus conradi is readily distinguished from the other representatives 

 of the genus from American strata. It is most nearly related to Cassidulus carolinensis, but 

 can be separated by its more excentric apical system and more transverse peristome and bj r 

 being narrower posteriorly and less concave around the peristome. Its nearest European ally 

 appears to be Pygorhynchus maveri de Loriol from the Tertiary of Switzerland, but the latter 

 has both its apical system and peristome less excentric anteriorly and does not have its peristome 

 transversely elongated. C. conradi also resembles. Pygorhynchus grignonensis (Defrance) 

 Agassiz from the Eocene of France, but is narrower posteriorly and has its apical system less 

 excentric anteriorly. 



Localities. — Palmyra, Lee County, Ga. (Conrad); Baker County, Ga. 



Geologic horizon.- — Upper Eocene or lower Oligocene or both. Conrad gave the matrix of 

 the form as white limestone. 



Collections. — Academy of Natural Sciences of Philadelphia (1078) ; Boston Society of Natural 

 History. 



Cassidulus (Pygorhynchus) carolinensis Twitehell, n. sp. 



Plate LXVII, figures 2a-g. 



Determinative characters. — Test thin walled, oval in marginal outline, posterior end trun- 

 cated; sides and anterior end rounded; upper surface convex, depressed, slightly more elevated 

 posteriorly than anteriorly and with a rather prominent low, rounded ridge above the periproct; 

 under surface flat, concave around the peristome; apex central or slightly excentric posteriorly. 

 Ambulacral areas narrow. A narrow granulated, median band back of the peristome. Apical 

 system excentric anteriorly; madreporite slightly tumid. Peristome excentric anteriorly, 

 directly beneath apical system, pentagonal, with a floscelle. Periproct elliptical, transverse, 

 supramarginal beneath an overhanging expansion of the test, whose edge is even with the 

 posterior margin. 



Dimensions. — Length 36 millimeters; width 32 millimeters; height 18 millimeters. This 

 specimen is about a fourth larger than the average. 



Description. — This species occurs in large numbers at several localities in North Carolina, 

 notably in association with Echinolampas appendiculatus. The test is thin walled, regularly 

 oval in marginal outline, the posterior end vertically truncated. The upper surface is uniformly 

 convex, depressed, sides and anterior end rounded, slightly more elevated posteriorly than 

 anteriorly and in the form of a low rounded ridge above the periproct; under surface flat, tumid 

 near the margin, concave around the peristome. The apex is central, or slightly excentric 

 posteriorly. 



