Descrijjfion of Some JSfew Species of Fossils. 99 



the muscles to be nearl}' united, and situated near the center; the 

 posterior pair are wideh' separated, and placed near the margin. 

 Length of specimen, 6 m. m. ; breadth, 5 m. m. ; convexity of upper 

 valve, 2 m. m. 



The peculiar surface ornamentation of this species will distinguish 

 it from all the others found within the Cincinnati rocks. 



Locality and Position. — Found associated with C jjarallela, at 

 Covington, Ky. 



Crania socialis, n. sp. (Plate IV., fig. 14.) 



Shell small, outline varying from subquadrate to subovate, and from 

 two to three times as wide as long; Dorsal valve very convex, or some- 

 times nearly flat on the top, with the shell immediately surrounding 

 the margin almost vertical, thereby imparting to the valve an angular 

 appearance; apex nearlj^ marginal, quite constant in its position, not 

 prominent. Frequently found adhering to crinoid columns. 



Surface, with from four to seven strong corrugations or ridges, run- 

 ning parallel with the length of the shell, which in most cases corre- 

 spond with the annulation of the crinoid stem to which it is attached. 



No markings were observed on the interior of this valve, excepting 

 the corrugations, which show through from the exterior. 



Length of medium sized specimen, 2.5 m. m. ; width, 6 m. m.; convex- 

 ity, 2 m. m. 



This form is apparentl}^ gregarious in its habits, one specimen of 

 crinoid stem before me, from the collection of Mr. E. B. Moore, having 

 more than twent}' specimens crowded within the space of one inch. It 

 differs from Crania scabiosa, Hall, to which it is most nearly related, in 

 form, and position of the apex, as well as in the surface markings. 



Locality and Position. — Found most common in the lower 200 ft. of 

 the Cincinnati Group, though ranging to about .350 above low water 

 mark at Cincinnati. 



TRINUCLEID^. 



Genus Trinucleus. 



Trixucleus bellulus, n. sp. (Plate IV., fig. 15.) 



Body small, nearly flat, and symmetrical. Cephalic shield about 

 three times as wide as long, subquadrate, with a distinct thoracic rino- 

 at the base, which is straight, with the posterior angles acutely ano-ular 

 or slightly rounded, and without any long spines ; glabella prominent 

 pyriform and produced posteriorh', into a long spine, reaching to the 

 pygidium; cheeks not as prominent as the glabella, triangular, and 

 finely punctate; marginal fillet wide, markod in front by from three to 



