Bracli'iopoda of the Cincinnati Group. 



Length of a large specimen, 1\ inches; breadth, If inches; convex- 

 ity, a little over one third of an inch. But specimens vary in their 

 proportions and differ widely in size. One specimen, four fifths of an 

 inch in length, one inch in width, has a convexity of one fifth of an 

 inch. 



This species, though widely dispersed, has a very limited range 

 (at about 700 feet above low water-mai'k) in the Cincinnati Group, 

 and is not particularly abundant at any locality. Richmond, Indiana, 

 is about as good as any locality for collecting it. 



Streptorlnjnclms vetvsta (James) vol. 1, p. 241, Cin. Quar. Jour, of 

 Sci., July, 1874, seems to be very closely related to this species. 



Hemipronites planwnhona — (Hall, 1847). 



Shell medium size, concavo-convex, semi-oval ; hinge line generally 

 longer than the breadth of the shell forward ; lateral extremities more 

 or less compressed and deflected ; lateral margins contracted poster- 

 iorly and rounded to the front, which forms a regular semi-circular 

 curve. 



Dorsal valve flat in the umbonal region, and rather strongly and 

 evenly convex in the central and anterior regions, from which it rounds 

 oflT abruptly to the front and lateral margins ; beak not distinct from 

 the edge of the sublinear area. Interior showing small cardinal pro- 

 cess, depressed, divided to its base into two diverging tooth-like parts, 

 flattened on their posterior faces and directed obliquely forward and 

 outward : socket ridges short and oblique ; mesial ridge low, extending 

 but a little distance forward, and the space between it and the socket 

 ridge, on each side, is occupied by a moderately distinct muscular scar. 



Ventral valve broadly and rather deeply concave in the central and 

 anterior regions, and slightly convex at the beak, which is very small, 

 scarcely projecting beyond the edge of the area and usually minutely 

 perforated ; area moderately high, extending the whole length of the 

 hinge ; flattened and inclined a little backward ; foramen closed by a 

 prominent, rounded, pseudo-deltidium, that is transversely striated, 

 and rather broadly sinuous in its inner edge for the reception of the 

 cardinal process of the other valve. Interior showing hinge teeth well 

 developed, trigonal and striated on their posterior sides ; dental lam- 

 inae extend forward from their inner bases, so as to nearly encircle the 

 saucer-shaped depression for the muscular scars, which is sometimes 

 divided by a small, linear mesial ridge ; cardinal margin prominent and 

 sharp within on each side of the hinge teeth ; anterior and lateral 



