782 THE CRINOIDEA CAMEEATA OF NOETH AMERICA. 



Interradials one or three in the first row, followed by one or two in the 

 second, all forming a part of the ventral disk. The large anal plate of the 

 dorsal cup is generally followed at the tegmen by two rows of three plates 

 each, and these by a large number of minute pieces, which enclose the anus. 

 The anal opening is directed laterally and placed near the upper end of the 

 anal area. The posterior oral occupies a central — or nearly central — posi- 

 tion ; it is highly protuberant, and very large compared with the other four, 

 which are small, scarcely convex, and pushed to the anterior side ; but 

 sometimes they may be \mrepresented altogether. In this case, small cover- 

 ing pieces follow the sides of the posterior oral; but when all the orals are 

 represented, generally large radial dome plates of a first and second order 

 take the place of the covering plates. 



Column round, small ; axial canal minute. 



Distribution. — Probably restricted to the age of the Warsaw and St. Louis 

 groups. 



T//pe of the genus : Talarocrinus cornigerus (Shumard). 



Remarks. — Talarocrinus forms a transition between Dicliocrinus and Ptero- 

 tocrinus. It preceded Pterotocrinus in geological time, while Dicliocrinus, 

 although surviving Talarocrinus, reached its climax before the latter was 

 introduced. The species upon which the genus was founded were originally 

 described by Shumard and Casseday and Lyon under Dicliocrinus, whence 

 S. A. Miller removed them to Pterotocrinus. 



Talarocrinus differs from Dicliocrinus in the more massive plates, and in 

 having but one costal to the ray. The latter is the case also in Pterotocrinus, 

 but the distichals in that genus are comparatively large, and form an import- 

 ant part of the cp\yx ; while those of Talarocrinus are small, and retain the 

 form of free arm plates. Besides, Pterotocrinus has large, wing-like appendages 

 fastened to the surface of the test, like which nothing is found in Talaro- 

 crinus ; the corresponding plates of the latter are much smaller and are 

 inserted between the other plates, instead of resting against their beveled 

 outer edges. 



