FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 215 



radiating and concentric striae, which differ in their character, according to 

 the places they occupy. On the baso-lateral area of each valve there are sub- 

 angular, abruptly elevated, concentric striae in their course from the anterior 

 margin to the umbonal ridge, where they terminate parallel to the anterior 

 and basal margins. These elevated striae have flat interspaces of different 

 width, sometimes three or four times as large as the striae. Some of these 

 interspaces are smooth, while others are occupied by one to three finer striae. 

 Between the umbonal ridge and the sinus, mentioned above as a shallow 

 depression crossing obliquely the valves, these interspacial finer striae become 

 more prominent, and some more are added by intercalation, thus causing them 

 to appear somewhat crowded. In this region, limited by the umbonal ridge 

 and the lateral sinus, the concentric striae are crossed by fine, closely arranged 

 radii, giving that portion of the surface a cancellated, somewhat rugose appear- 

 ance. This cancellated belt commences at the apical end of the umbonal ridge, 

 increases regularly, but rapidly in width, until it occupies, in the basal margin, 

 the whole posterior half of the shell. 



The dorsal incline is covered by subequal, rounded, and closely set radii, 

 which start from the posterior portion of the cardinal line, and extend along 

 the cardino-posterior margins to the umbonal ridge ; they increase in number 

 by bifurcation and interpolation. 



I do not know any other Goniophora, and can not, therefore, compare this 

 species with any of its congeners. Prof. Hall compares it with G. perangulata 

 of the Schoharie grit, with which he thinks it may be identical. In comparing 

 my specimens with his figures of that species, it appears to me that there is a 

 vast difference between both species. 



Formation and Locality. This shell occurs in the Corniferous limestone of the Deronian forma- 

 tion in Kentucky and Indiana, at and around the Falls of the Ohio. It is a very rare shell ; the two 

 specimens in my own collection are, so far, the only individuals found in our rocks. 



Genus Modiomorpha. Han. 



Modiomorpha, Hall. Prel. Notice of Lam. Shells 1870. 



Etymology : Contracted from modiola, a genus of shells ; and morphe, form or shape like Modiola. 



Shell inequivalve, very inequilateral, compressed, sub-ovate in outline, 

 largest posteriorly; beaks small, compressed, usually situated within the 

 anterior third of the length. Surface of shell marked by rugose or undulating 

 concentric striae, which usually coalesce or become fasciculate toward the 

 anterior end. The valves are crossed obliquely by a more or less distinctly 

 defined sinus passing from the beak to the base, and constricting the basal 

 margin ; the anterior end is rounded, forming a projecting lobe of greater or 

 less extent beyond the beak. Hinge characterized by a single, strong, wedge- 



