35 



In each regular iuterradial area there is a large central plate, 

 which is surrounded in some areas by seven plates, and, in other 

 areas, by eight plates, and above these there are three or four 

 plates that may be said to belong to the calyx, but they graduate 

 into the plates of the vault without auy distinct line of separation. 

 In fact, the area is continuous with the vault. The azygous in- 

 terradius differs from the other areas only in being a little wider 

 and containing a few more plates. The central plate is some- 

 what larger than in the other areas and slightly truncates the 

 subradial, and is surrounded with eight other small plates. On 

 each superior lateral side of the ring thus formed by the eight 

 plates, there are four plates, and above these there or three or 

 four plates that may be said to belong to the calyx, but they 

 graduate into the plates of the vault without any line of sep- 

 aration. 



The vault is moderately convex over the ambulacral canals and 

 slightly depressed in the interradial areas. It is covereel with 

 rather large polygonal plates, each of which bears a central node. 

 Part of the matrix is on the summit of our specimen so as to 

 present the delineation of all the plates, as may be seen in the 

 illustrations. There is a small subcentral proboscis. 



This species is distinguished by its interradial areas alone from 

 all other described species. Indeed, it is quite peculiar in many 

 respects, and no comparison is necessary with any that has been 

 described. 



Found by Prof. A. G. Wetherby, in the Trenton Group, in Knox 

 county, Tennessee, and now in the collection of Wm. F. E. Gur- 

 ley. 



GILBERTSOCRINUS GBEENEI, n. Sp. 



Plate III, Fig. 13, basal view; Fig. 14, side view: Fig. 15, stim- 



mit of the same specimen, port of the vault is hrohni 



niray and two j^ieces are chippeil fmtti the Ikisc. 



Calyx broadly truncated at the base and summit, subpentagonal 

 in transverse section, constricted below the arms, height and width 

 subequal. liadial ridges rounded. Spines on the first radials 

 directed downward at an angle of forty-five degrees, and base de- 

 pressed so the calyx will rest on the points of these spines. The 

 first interradials are also spine-bearing and all other plates slightly 

 convex. Column round and pierced by a cinque foil canal. 



