300 Wood — Crinoid from the Hamilton of Charleston) n, 2nd. 



The plates of the posterior area are irregular in shape and 

 have live, six, or seven sides. Of the three plates resting upon 

 the primary anal two are hexagonal and one pentagonal. 



The plates of the tegmen do not vary greatly in size, the 

 orals being only slightly larger than the others. 



Formation and locality. — This species is found in lime- 

 stones of the Hamilton Group at Charlestown, Indiana. 



The species here described is closely related to Actinocrinus 

 (Genimocrinus) comigeras Lyon and Casseday, but it differs 

 from the latter in the presence of three instead of two inter- 

 palmars, the absence of a central spine on the tegmen and of 

 crescentic ridges on the radials. According to the original 

 description of G. cornigerus the plates of the posterior area 

 resemble those of the Actinocrinidae, that is one hexagonal 

 primary anal followed by two plates ; but this species is 

 regarded by Wachsmuth and Springer as synonymous with 

 G. Ttentuckiensis, in which the primary anal is heptagonal and 

 bears three plates as in G. carinatus. G. Ttentackiensis differs 

 from the latter species in the number of distichals which is 

 2X10 instead of IX 10, and in the arrangement of the palmars 

 and interpalmarsthe axillary distichals supporting 2X4 palmars 

 in each ray, and the three interpalmars being in two rows 

 instead of one. From both G. hentnckiensis and G. eucharis 

 the present species differs in the nearly equal size of second 

 costals and radials, in the number and arrangement of the 

 higher plates of the posterior area, and in several other 

 important respects. 



Actinocrinus asper Lyon bears an angular ridge on the 

 lower portion of the radials which under favorable conditions 

 of preservation might resemble the petal-like ornamentation 

 of the radials in Gennceocrinus carinatus, but the basal plates 

 are not thickened as in the latter species, the costals are very 

 small in comparison with the radials, and each plate of the 

 tegmen bears a strong node. 



Gennmocrinus carinatus appears, therefore, to possess an 

 association of well marked and peculiar features which entitle 

 it to be considered a distinct species. 



Geological Department, 

 Massachusetts Institute of Technology. 



