1881.] NATURAL SCIENCES OF PHILADELPHIA. 381 



number of small irregularl}^ arranged plates, which decrease in 

 size rapidly toward the peripher3\ At the edge of the vault there 

 are twenty ambulacral openings, ten of which are larger and con- 

 necting with the ten appendages, the ten smaller ones with their 

 first lateral arm. Apical dome plates well developed, much larger 

 than the rest of the plates, and more convex. Anus excentric, in 

 form of a simple opening. 



Column heavy, round, sometimes with lateral excrescences; 

 central canal large, pentalobate. 



Geological Position^ etc. — The only known species of this genus 

 occurs in the Stringocephalenkalk of the Eifel. 



1826. Bipidocrinus crenatus Goldfu^s. (Ehodocr. crenatus) Petref. Germ., i, p. 

 211, PI. 64, fig. 3; also Agassiz, 1835, Soc. Neuchat., i, p. 196; Roemer, 

 Verb. Naturh. Verein f. Rheinl., viii, p. 358, PI. 1, fig. 1, and Lethsea Geogn. 

 ii, p. 241, PI. 4, figs. \1, a-b; Pic'et, 185J, Traite de Paleont, iv, p. 314, PI. 

 100, fig. 10: Schultze, 1867, Echin. Eifl. Kalk, p. 53, PI. 7, figs. 1 a-n ; 

 Zittel, 1879, Handb. der Palseont, p. 377, fig. 263. Devonian. Eifel, Germ. 

 Syn. Bhodocr. tessellatus Steininger. Geogn. Beschreibung der Eifel, p. 36. 



10. THYLACOCEINTJS Oehlert. 



1878. Oehlert. Extract du Bull. Soc. Geol. de France (ser. 3), vii, 



(November No.). 



1879. Zittel. Handb. d. Palaeont., i, p. 375. 



This genus was placed by Zittel among his Glyptocrinidae, but 

 it agrees much closer with some species of Bhodocrinus, from 

 which it differs in having very much longer, heavier and undi- 

 vided arms. This difference would perhaps entitle it only to a 

 subgeneric rank, if not the arms in the Rhodocrinidse generally 

 were short, thin and bifurcating. 



Generic Diagnosis. — Body large, globular. Calyx inflated at 

 the lower part, somewhat constricted toward the arm regions; 

 plates thin, convex, without special ornamentation ; symmetry 

 almost equilateral. 



Underbasals five, small, forming a pentagonal disk. Basals 

 five, hexagonal, upper and lower sides parallel, the lower resting 

 against the straight sides of the inner pentagon, the upper sup- 

 porting the first interradials. Primary radials 3X5; the first 

 hexagonal ; the second larger than the first ; the third supporting 

 2 X 10 secondar}^ radials, and these in turn the arms. 



Arms heavy, extremel}' long, five or six times the height of the 

 calyx, simple throughout. The proximal joints are single, quad- 



