140 ECHINODERMATA—PELMATOZOA SUB-KINGDOM III 
Family 2. Hexacrinidae. Wachsmuth and Springer. 
Dorsal cup composed of a monocyclic base, five large radials, and an anal plate 
similar in form and size to the radials interposed between them. In all other respects 
constituted like the Platycrinidae. Devonian and Carboniferous. 
Hevacrinus, Austin (Fig. 241). £ three, equal; £& five, very large and 
elongate. Tegmen low, composed of relatively large plates, and pierced by an 
eccentric anal opening. Arms uniserial or biserial; pimnules unusually long. 
Column round. Devonian; represented by numerous species in England, 
France, Belgium, and the Eifel, but by only a few in North America. 
Dichocrinus, Miinst. Differs from Heaacrinus in having but two hexagonal 
basals, and an eccentric anal opening. Sub-Carboniferous ; Belgium. Great 
Britain, and North America. 
Arthrocantha, Williams (Histricrinus, Hinde). Like Hexacrinus, except that 
the calyx plates are beset with short mobile spines. Devonian; North 
America. 
Pterotocrinus, Lyon and Cass. 6 two, equal. short, rapidly spreading ; 
their upper faces excavated for the reception of several orders of brachials, 

Fic. 241. 
Hexacrinus elongatus, Goldf. Devonian; Pelm, Hifel. a, Calyx seen from one side; b, Aspect of summit ; 
c, Diagram of calyx and arms; d, e, Column of JI. spinosus, Mill. (after L. Schultze). 
which rest with their lateral edges upon it; all of these plates taking part in 
the dorsal cup. JRA less than half the size of the £, and sometimes 
triangular. Tegmen highly elevated, pyramidal. Orals large, asymmetrical ; 
their lower angles enclosing five large, radially disposed plates, which are 
separated from one another by interambulacral pieces. These plates are 
provided with enormous, leaf-like, club-shaped, or spatulate processes, which 
project outward conspicuously from between the arms. Anus sub-central. 
Arms four to each ray ; biserial. Kaskaskia Group ; North America. ) 
Talarocrinus, W. and Sp. Intermediate between the preceding and Dicho- 
crinus ; structure of the tegmen resembling the former, that of the dorsal cup 
the latter. JRA slightly smaller than the f, its upper end narrower than 
