484 THE CRIJSTOIDEA CAMERATA OF NORTH AMERICA. 



vertical ridge, whicli extends above the arm regions, enclosing tlie anal 

 opening, which is directed laterally. Interdistichal spaces deeply grooved, 

 and occupied by a single minute piece. Ventral disk low, slightly convex, 

 pentangular in outline. The ambulacra are tegminal and raised above the 

 general level of the disk ; the food grooves covered by two rows of compara- 

 tively stout pieces with a large nodose plate above each bifarcation. Pos- 

 terior oral proportionally large, extended into an elongate node ; the four 

 others barely convex. Column small ; the axial canal minute. 



Horizon and Locality. — Hamilton group ; Louisville, Ky., Clark Co., 

 Ind., and Alpina, Mich. 



Tj/pes in the Knapp collection at New Providence, Ind. 



Hemarhs. — From Hall's descriptions it seems to us probable that his 

 Actinocrimis caiiHctihis, A. pra'ciasor, A. pocilhm, and A. calyjoso, from the 

 Hamilton group of the State of New York, are all or in part identical with 

 this species. As neither one of them is figured, and the tj'pes in the State 

 Museum of Albany are not accessible to us, we are unable to make the neces- 

 sary comparison. In 1881 we erroneously placed this species under Gennceo- 

 crinns. A subsequent comparison with the types shows clearly that it has 

 essentially the characteristics of Aorocrinus. 



BARRANDEOCRINUS Angelin. 

 Plate VIII. Fig. 1. 



1873. Angelih; Iconogr. Cria. Suec, p. 7. 



18S5. W. and Sp. ; Revision Paleeocr., Part III., p. 125. 



The calyx in perfect specimens is invisible, being completely enveloped 

 by the arms and pinnules, which hang down over it ; and the specimens, when 

 all the arms are in place, have a superficial resemblance to a Blastoid. The 

 calyx is composed of comparatively few plates, and resembles Dorycrinus in 

 the form of the dorsal cup, from which it differs essentially in the structure 

 of tegmen and arms. 



Basals three, large. Radials quite irregular in outline ; the posterior 

 ones pentangular, the anterior one hexagonal, and the remaining two hep- 

 tagonal. Costals two, the axillary very small, subtriangular, its upper angle 

 sharply pointed. Distichals apparently but one in the calyx. Arms ten, 

 very heavy, biserial, folding outward and recumbent over the calyx, cover- 

 ing the latter completely, and leaving of the arms only the pinnules exposed 



