18 PROCEEDINGS OF THE AMERICAN ACADEMY 



said above, has with the bifurcations 8x5 = '40. D. comigerus 

 which differs considerably from all other species, has 4X5 = 20. 

 D. jicus has six pairs, 6 X 2 = 12, again bifurcating on the first 

 joint, producing twenty-four arms or fingers. We may readily sup- 

 pose that the greater number of the species of this genus have five 

 pairs of arms, bifurcating once or more. The arms are long, fimbri- 

 ated, and composed of cuneiform pieces, either in single or double 

 rows. 



Inter-radials. Shumard is the only author who notices inter-radials. 

 He says, that " from four to five exist in two of his species, they rest 

 on the oblique superior lateral edges of the radial plates." They 

 might easily be mistaken for the lower pieces of the vault. 



We propose, then, the following formula for Dichocrinus : — 



Basal pieces .... 2 



Eadial pieces . . . 1 to 3 X 5 



Inter-radial pieces . . . 4 to 5 X 5 



Anal pieces . . . • 1 to 5 



Arms 5 pairs, bifurcating. 



Columns round. 



The vault, in all the specimens where we have seen it preserved, 

 is large, high, and more or less ornamented with thorns and salient 

 tubercles. This genus differs so markedly from the genera Platy- 

 crinus and Hexacrinus, both in the more elongated form, the bipartite 

 basis, and its deep angular notch on the anal side, that it admits 

 of an easy distinction. It approaches quite nearly to Cotyledonocrinus 

 and Pterotocrinus, having like them a bipartite base, with a series 

 of large pieces about it. Cotyledonocrinus has only five pieces arising 

 from the basis, instead of six, the arms are non-bifurcate ; the differ- 

 ence between this genus and Pterotocrinus is so marked that they 

 cannot be confounded. 



Dichocrinus poltdactylus, Sp. Nov. 



Body. Subconoidal, resembling the ornate capitals of some com- 

 posite columns, spreading rapidly from the base, the upper portion 

 marked by prominent folds of salient tubercles. The whole of the 

 pieces of the calyx are thin. 



Vault. Surmounted by a large proboscis : column small, subrotund. 



Basal pieces. The two basal pieces are large, spreading rapidly 



