256 PROCEEDINGS OF THE ACADEMY OF [1881. 



the strength of Austin's figure. On the other hand, Shumard 

 described his two species, D. cornigerus and D. sexlohalus, with a 

 single large radial, and none above it. Casseda}' and Lyon state 

 the number of radials as 1 to 3 X 5, in which opinion Meek and 

 Worthen coincide. 



We have no doubt that the latter statement is correct, and that 

 Austin's species is incorrectly figured, and had actually but three 

 radials ; but we have ascertained from several excellent specimens 

 loaned to us by Prof. Worthen, that the so-called D. cornigerus 

 and D. sexlohatus of Shumard both have a very minute second 

 radial, which is sometimes not visible externally. These two 

 species, however, like some others described by Casseday and 

 Lyon, differ from the typical Dichocrinus in several other import- 

 ant points, and this has led us to arrange them in a new generic 

 group under Talarocrinus^ which includes every species of this 

 form with only two primary radials. We have examined all 

 known American species of Dichocrinus proper, and find they all 

 have three primary radials. 



Revised Generic Diagnosis. — Cal^'X deeply cup-shaped ; plates 

 delicate, rarely ornamented ; S3mmetry distinctly bilateral. 



Basals two, hexagonal, forming together an obconical or rounded 

 cup. Radials 3X5. The five plates of the first series very 

 large, their sides straight and nearly parallel ; two rest on each 

 basal piece, the anterior plate in a notch at one end of the basal 

 suture ; against the opposite end there rests a large anal plate, 

 which is placed in line with the first radials. Succeeding radials 

 very small, occupying scarcelj^ more than one-fourth the width of 

 the first. The third radials are bifui'cating plates which support 

 either the arms, or in species with more than ten arms, the higher 

 orders of radials. Secondary, tertiary, or even quarternar}' 

 radials occur according to the number of arms. These higher 

 orders are generally in series of two plates each, exceptionally 

 three ; they are similar in appearance to ordinary arm plates, but 

 are easily distinguished by being single-jointed ; while the arm 

 plates, from the base up, are composed of a double series of 

 pieces. 



Arms rather delicate, but they give off" very long and stout pin- 

 nules composed of large joints. The pinnules form a very char- 

 acteristic feature of the genus. 



Anal plate almost as large as the first radials, often narrower 



