10 



side toward the central part of the body, which readers it prob- 

 able that they are furrowed within so that a transverse section 

 would be somewhat V-shaped, though they are depressed on the 

 dorsal side. In no part of this rim is there any evidence of 

 pectinated rhombs, pores or arms. 



On the dorsal side of our specimen, there are only five plates 

 preserved within the marginal rim, but figure 4 shows there are 

 seven plates, two of which abut upon the column. The three su- 

 perior plates are subconical. The outer surface is destroyed by 

 silicificatiou. 



On the ventral side, there are evidently more plates within the 

 marginal rim, but part of them cannot be distinguished, in our 

 specimen, because the silicification lias obscured the sutures. The 

 ventral side is much more convex than the dorsal. The single 

 arm to which AVetherby referred arises between plates, within the 

 marginal rim of plates, and not from the apex of the body by 

 any means. This is shown by his illustration as well as by ours. 

 We cannot distinguish the arm plates, in our specimen, but the 

 projection seems to be that of an arm. We are not able to dis- 

 tinguish any openings, but the tubercle, to which Wetherby re- 

 ferred, is on the left of what we hav(^ called the column, though 

 it is not shown in our illustration, aud we are not sure that it 

 indicates anything beyond the convexity of the plate. 



Found in the Trenton Group, in Mercer county, Kentucky, and 

 now in the collection of Wm. F. E. Gurley. 



Family CARYOCRINID.E. 



CARYOCKINUS ELLIPTICUS, n. sp. 



Pltite II, Fig. IS, anievior side virin; F'kj. li, sutiimil ricw. 



Species below medium size, subelliptical in outline, somewhat 

 angular below, but round in tlie central part. Sharp ridges radi- 

 ate from the center of the plates to each angle, except on tlie 

 basal plates, where a sharp ridge runs from each of the two supe- 

 rior angles on each plate, to the point of columuar attachment. 

 There is a single row of pores on each side of these angular 

 ridges, but none elsewhere on the plates. 



The four basal plates are of une(|ual size and form a cup less 

 than one-tliird the length of the boily. Tlic strong longitudinal 



