1879.] NATURAL SCIENCES OF PHILADELPHIA. 295 



longitudinally arranged. Each of them contains a rather deep 

 furrow, which in perfect specimens is arched over by a row of 

 wedge-shaped plates which stand out prominently and appear very 

 much like pinnulse. 1 



Arms bifurcating frequently, gradually tapering; arm pieces, 

 like the free radials, all projecting at the upper edge, thereby pro- 

 ducing a sort of imbrication. Pinnulse unknown. 



Column strong, distinctly pentagonal, the angles in line with 

 the radial plates of the body. 



Geological position. Lower Silurian. 



The following two species are the only examples of this genus: 



*1865. Iocrinus crassus Meek & Worthen. (Heterocr. crassus), Proc. Acad. 



Nat. Sci. Phila., p. 147; also Geol. Rep. 111., vol. iii. p. 325, pi. 4, figs. 



1 a-c ; also vol. v, pi. 23, fig. 1. Hudson River Gr Oswego, 111. 

 *1865. Iocr. subcrassus Meek & Worthen. (Heterocr. subcrassus), Proc. Acad. 



Nat. Sei. Phila., p. 148; also Oeol. Rep. 111., vol. iii. p. 325, pi. 4, figs. 



5 a-d ; also Meek, Heterocr. (Iocrinus) subcrassus, Geol. Surv. Ohio, Pal., 



vol. i. p. 15, pi. 1, figs. 9 a, b. Hudson River Gr. Cincinnati, Ohio. 

 Syn. Heterocr. (?) Iocrinus polyxo Hall, 1866. 24th Rep. N. Y. St. Cab. 



Nat. Hist., p. 210. 



3. ANOMALOCRINUS Meek and Worthen. 

 (Diagram PI. 16, Fig. 1.) 



1865. Heterocrinus (?) (Anomalocrinus) Meek & "Worth. Proc. Acad. 

 Nat. Sci. Phila., p. 148. 



1868. Hybocrinus? {Anomalocrinus) Meek & Worth. Geol. Rep. 111., 



vol. iii. p. 327. 



1869. Ataxocrinus Lyon. Am. Philos. Soc, vol. xiii. p. 464. 

 1873. Anomalocrinus Meek. Geol. Surv. Ohio, Pal., vol. i. p. 17. 



Generic Diagnosis. General form of the crinoid depressed, 

 cal} r x comparatively large, depressed subglobose ; its form ex- 

 tremely irregular, scarcely two plates being of the same shape. 



Underbasals unknown, and perhaps undeveloped. Basals five, 

 small, subequal, pentagonal, wider than high, partly hidden by the 

 column. Radials very large, of diverse forms, simple or compound, 

 the latter divided either horizontally or vertically. Of the com- 



1 It was to this peculiar structure that we alluded in our remarks on this 

 family, and the similarity in the appearance of the ventral sac and the arms 

 and pinnulo? is indeed most striking. If there is in nature any such thing 

 as a transmutation of one organ into another, it would seem that such was 

 the case here, and this may lead to a better understanding of the functions 

 of the ventral sac. 



