Brachiopoda of the Cincinnati Group. 35 



adult examples ; its greatest convexity being, generally, a little behind 

 the middle, on each side of a shallow, undefined mesial sinus, generally 

 extending from the front to the umbonal region, but sometimes nearly 

 or quite obsolete, or only represented by a slight flattening along the 

 middle ; swell of the umbo comparatively prominent, and often pro. 

 jecting backward further than the beak of the other valve ; beak rather 

 strongly incurved ; area of moderate height in the middle, but sloping 

 to the lateral extremities, sharp along the margin, and more or less 

 strongly incurved, foramen broad, triangular, and not closed by the 

 cardinal process. Interior with scars of the adductor muscles situated 

 on each side of a low mesial ridge, which is narrower between the 

 anterior than the posterior pair, which latter are placed far back under 

 the brachial processes, and rather strongly striated, but without well 

 defined margins ; anterior pair somewhat trigonal, and usually each sep- 

 arated from the posterior by an obscure transverse ridge, but without 

 well defined anterior margins ; cardinal process merely presenting the 

 appearance of a compressed or sharp ridge, much lower than the surface 

 of the cardinal area ; sockets distinct ; brachial processes directed 

 forward, and more or less laterally, usually sharp on their inner under 

 edges ; vascular scars unknown. 



Ventral valve most convex at or near the apex of the beak, from 

 near which it slopes more rapidly to the front and lateral margins than 

 to the anterior lateral, the anterior region being impressed so as to 

 form a broad, more or less deep, undefined mesial sinus, that dies out 

 before reaching the umbo ; beak rather elevated, but not projecting 

 backward, abruptly pointed very nearly straight, or sometimes slightly 

 arched at the point ; cardinal area rather high at the beak, but sloping to 

 the lateral extremities, flat or slightly arched, and usually standing nearly 

 at right angles to the plane of the valve ; foramen generally higher 

 than its breadth at the hinge line, and extending to the apex of the 

 beak. Interior showing the cardinal margin to be prominent and 

 sharp, and the hinge teeth well developed ; cavity for the reception of 

 the muscular scars deep, nearly or quite reaching the middle of the 

 valve, obcordate in form, and bounded by a prominent ridge, continued 

 forward from the bases of the hinge teeth, and curved a little back- 

 ward at the central point of the front, where they meet impressions of 

 the divaricator muscles (cardinal of some) deep ; while those of the 

 adjustors are so small, and pushed so far aside, as to occupy the sides 

 of the dental plates, and thus to be out of sight in a direct view ; those 

 left by the adductors are narrow, elongated, and situated on each side 

 of a mesial ridge, that is divided along the middle by so wide and 

 distinct a furrow as to appear almost like two linear ridges ; transversely 



