378 PROCEEDINGS OF THE ACADEMY OF [1881- 



Angelin's Calyptocrinidae, with which it has some superficial 

 resemblance in the form of the calyx, and in the arrangement of 

 the radial and interradial plates, but from which it is otherwise 

 very distinct. Its closest affinities are with Ripidocrinus Bey rich, 

 in which, however, the arms are very ditferentlj^ constructed. 



Generic Diagnosis. — Form of calyx depressed, subglobose, or 

 nearly hemispherical ; symmetry more or less perfectly equilateral. 

 Plates heavy, their surface flat or sometimes a little concave, 

 smooth, or finely granulose. Yault very low, scarcely rising above 

 the height of the calyx. 



Underbasals five, very small, abruptly and deeply depressed, 

 concealed by the column. Basals five, of uniform size, either 

 heptagonal and supporting upon the upper truncate side the first 

 interradial, or four of them hexagonal, angular above, and only 

 the posterior one truncate for the support of the first anal plate. 

 Primary radials 3X5, of nearly equal size ; the first pentagonal; 

 the second and third hexagonal. The latter is truncate above, 

 and supports within the axil of the secondary radials which are 

 given oflT from the upper sloping sides of the primary radials, 

 a comparatively large, elongate, hexagonal interaxillary plate, 

 which extends to the height of the first arm joints. Secondary 

 radials 2X10, the first large, pentagonal, the second shorter, and 

 supporting the arms. 



Interradial plates four to five, in three series ; the first large, 

 heptagonal ; the two plates of the second series a little smaller 

 than the first, but yet comparatively large ; the third series small, 

 composed of one or two plates, which are enclosed by the secon- 

 dary radials. The anal area is frequently not distinct from the 

 four others, but it has occasionally three plates in the second 

 series. The plates of the lower calyx are of about uniform size, 

 but the last secondary radials, the interaxillary, and the upper 

 series of interradial plates are considerably smaller. 



Vault almost flat, composed of a large number of convex plates, 

 which are depressed in the interradial regions. Anus subcentral 

 or excentric, in form of a strong tube, constructed of similar 

 plates as the vault ; length unknown. Apical dome plates well 

 defined, twice as large as the other vault pieces. Ambulacral or arm 

 passages directed upward, and passing at the edge through the 

 vault. Arms ten, which remain simple, placed wide apart, strong, 

 gradually tapering to the tips, and constructed, from the radials 



