FOSSIL CRINOIDS. 149 



Rays not branching beyond IIBr 



Brachials quadrangular, uniserial 



Ventral sac large Graphiocrinus. 



(Synn. Phialocrinus, Aesiocrinus.) 

 Brachials biserial 



Ventral sac inconspicuous Delocrinus. 



No anal x between RR. 



Brachials biserial 



Ventral sac inconspicuous or wanting 



IBB undivided Stemmatocrinus. 



IBB small, covered by stem 



Anal X rests on upper surface 



of post. RR Erisocrinus. 



No anal x or tube plate visible .... Encrinus. 



PoTERiocRiNUS J. S. Miller. 



1821. A Natural History of the Crinoidea, 65. 



1879. Wachsmuth and Spbinger, Rev. Pal., 104, where the intervening synonymy is given. 



Revised generic Diagnosis. 



Inadunate; dicyclic; pinnulate. Articulating facets semicircular, not 

 filling distal face of radials, usually with straight transverse ridge. Radianal 

 obliquely to left of right posterior radial; anal x and first tube plate within 

 dorsal cup. Primibrachs 1 or 2. Arms dichotomous, long, branching fre- 

 quently. Ventral sac large and long, tapering to the distal end. Calyx plates 

 usually folded into strong plications. Column round. 



Genotype. Poteriocrinus crassus Miller. 



Distribution. Devonian to Lower Carboniferous. Europe and America. 



Miller's description of his type species, P. crassus, is excellent, even to noting 

 the anal plates, which he did not understand but supposed to be due to irregu- 

 larity. In spite of all the confusion thrown around it by subsequent authors, 

 his figures give such a fair idea of the strongly plicated plates, and the exact 

 form and construction of the articulating facets, that there should be no hesi- 

 tation in recognizing the generic type. It is readily identifiable from isolated 

 plates in the Belgian Lower Carboniferous, although, as before observed, the 

 specimen figured by de Koninck and Lehon as P. crassus is deformed, and per- 

 haps does not belong to it. The Austins (Mon. Rec. and Foss. Crin., 74) say that 

 Miller's principal figure opposite p. 68 is a restoration made from the original 



