lOO PALAEONTOLOGY OF NEW-YORK. 



The muscular impressions consist of a narrow central scar just below 

 the apex of the beak, for the occlusor muscles, with a central elongate 

 oval scar marking the place of the divaricator muscles ; while there are 

 two elongate ovate or pyriform scars, one on each side of the apex, and 

 spreading laterally just within the limit of the constricted line, figure 7/. 



The figures 7 a -J" illustrate the usual form and convexity of the species. The character of 

 the cast of the ventral valve is shown in figures 7 e,f, where the marks of the internal 

 tubes of the area are conspicuous. 



The cardinal spines are rarely visible, owing to the incurved margin which usually Icavca 

 these appendages imbedded in the stone. In one specimen, however, five or six spines 

 are seen on one side of the apex. The shell of the area is penetrated from the interior 

 by numerous comparatively large cylindrical tubes, some of which terminate in elon- 

 gate spines upon the exterior margin. In one specimen, fifteen of these tubes may be 

 counted on one side of the apex. In the casts or partial casts of the shell, these tubes 

 give the appearance, of coarse crenulations. 



This species is distinguished from C. hemispherica by being a little less promi- 

 nent on the umbo, and by the shallow sinus, as well as the more numerous and 

 much finer strias. The cast does not preserve the marks of the striae so conspicu- 

 ously, while the surface is more abundantly pitted, without being sensibly 

 arranged in distinct lines. 



Geological formation and locality. This species has been found only in the Cor- 

 niferous limestone, near Williamsville and Clarence-hollow in Erie county, N. Y. 



Clionetes acatiradiata. 



PLATE XX. . 



Strophomena acutiradiata : HAit, Geol. Report 4th District New York, p. 171. 1843. 

 CKonttet acutiradiata .- Hall in Tenth Keport on the State Cabinet, p. 117. 1857. 



Shell nearly semicircular, sometimes a little more than twicei as wide 

 as long; the cardinal extremities produced. 



Ventral valve moderately convex, sometimes a little gibbous in the 

 upper part, and frequently flattened or depressed at and below the 

 middle : umbo little elevated above the hinge-line ; greatest convexity 

 above the middle, from whence it curves gently to the front, somewhat 

 abruptly depressed towards the cardinal extremities, which are subau- 

 riculate and nearly flat. In two individuals, there is a distinct longi- 

 tudinal sinus in the middle of the valve. 



