478 FRANK SPRINGER 



I have five specimens suitable for this study — two from the original 

 locality at White's Creek Springs, Tenn., and three from near Louis- 

 ville, Ky. Four of them have all the rays visible, and they all show 

 perfect symmetry below the first bifurcation, the rays having uni- 

 formly the radial and two primibrachs, without any radianal. In 

 these specimens there is some irregularity in the secundibrachs, one 

 having 4-4 in all rays, and the others having 4-4 in some rays and 

 4-3 in others. In another specimen the rays are not fully preserved, 

 but the condition is such that, in addition to the radials and some 

 primibrachs, they show the basals and infrabasals very plainly, both 

 internally and externally, and there is no radianal. In the type 

 specimen, however, from the Troost collection in the National 

 Museum at Washington, which preserves all rays' intact, there is 

 an extra plate in one ray, which has radial and three primibrachs, 

 while all the others have two primibrachs, with variations of 4-3 to 

 4-4 secundibrachs. The infrabasals are not visible, and it is impos- 

 sible to judge whether the extra plate is in the right posterior ray or 

 not. The lower plate in the ray having the extra one is of the same 

 size and shape as the lower plate in the other rays, and does not 

 exhibit the difference which characterizes it in the Silurian specimens. 

 In view of the uniform absence of a radianal in all other Carbonif- 

 erous specimens, I think we are warranted in considering the pres- 

 ence of an extra plate in this one as a case of sport — just as we have 

 in some specimens an occasional straggling interbrachial. 



In /. greenei, from the Keokuk Limestone of Indiana, only three 

 rays are visible, each of which has the radial and three primibrachs. 



What the condition of the genus was in the Devonian we do not 

 know. It is supposed to occur in the Chemung of New York, but 

 all the specimens that I have seen are too imperfect to afford any 

 information. If any reader of this paper should possess a specimen 

 of Ichthyocrinus from the Devonian, with the base or all five rays 

 preserved, I should esteem it a great favor to be advised of the fact. 



The result, therefore, of the examination of actual specimens 

 considered to be Ichthyocrinus is: 



1. All Silurian specimens, without exception, have a radianal in 

 primitive position under the right posterior radial. 



2. All Carboniferous specimens (with the solitary ex ;eption above 



