736 THE CRINOIDEA CAMEEATA OF NORTH AilEEICA. 



somewhat larger, with only two arms like " Platycrimis " retiarius, but 

 these beautifully sculptured. All these species, including Cordylocrinus com- 

 tus, agree in the basals and radials with PMycrinus, but have two costals 

 instead of one, and their arms are uniserial as in the young Platycrimis, their 

 pinnules large and not in contact laterally. The only point of doubt, and 

 upon which possibly a generic separation from the Gotland form might be 

 justified, is that the American and Dudley specimens have whorls of cirri 

 from all their nodal joints, which are not indicated in the Swedish Cordylo- 

 crinus comtus. However, cirri may have been represented also in that 

 species, and until their absence is satisfactorily proved, we must refer all the 

 above forms to that genus. The interradial plates, which Angelin described 

 as distributed in three series, in .all those species form a part of the disk, 

 only the lower one resting between the brachials. Hall describes a " probos- 

 cis " in " Platycrimis " 2^litinosus, which is imperfectly shown in the specimen, 

 and it is possible that the other species have a similar structure. We propose 

 the following generic diagnosis : — 



Basals and radials as in PMycrinus. Costals two, narrow, attached to a 

 small facet. Arms from two to four to the ray. When four, the last bifur- 

 cation takes place from the sixth, or as high as the ninth distichal. The 

 arms are long and uniserial ; composed either of wedge-form plates alter- 

 nately arranged, or of quadrangular, transverse pieces. Pinnules stout and 

 long, not in contact. The first interradial plates resting against the costals. 

 Column round, with numerous internodal joints, and cirrus-bearing. The 

 cirri very long, directed upward, the upper ones rising to almost half the 

 height of the crown, and arranged in whorls of three to four to the arm 

 joint. 



Distribution. — This genus is restricted to the Wenlock group in England 

 and Sweden, and to the Upper Helderberg in America. 



Type of the genus : Cordyhcrinus comtus Angl. 



