Brachiopoda of the Cindmwiti Group. 21 



perhaps, always a little shorter thau the greatest hreadth of the valves ; 

 lateral margins generally rouudiug to the hmge, most promment at, or 

 a little behind, the middle, and rounding to the front, which is usually 

 somewhat straightened, or very faintly sinuous at the middle; or, 

 presents a regular semi-circular outline. 



Dorsal valve i^arly flat, or slightly convex on each side of a shallow, 

 mesial sinus, that commences very narrow at the beak, and usually 

 widens rather rapidly to the front; beak very small, scarcely projectmg 

 beyond the edge of the area, and not incurved ; area low at the middle, 

 and narrowing off to nothing at the lateral extremities of the hinge, 

 slightly arched, and directed obliquely backward; foramen very 

 small, and filled by the cardinal process. Interior very shallow, and 

 provided with a slender mesial ridge that extends about half way 

 forward from the hinge, between the muscular impressions, which are 

 not usually well defined ; scars of posterior pair of adductor muscles 

 smaller, and usually deeper, than the anterior, and situated close buck 

 under the brachial processes ; those of the anterior pair three or four 

 times the size of the posterior, suboval in form, and extending to 

 near the middle of the valve ; cardinal process very small and trifid ; 

 brachial processes, comparatively, rather stout and prominent ; inter- 

 nal surface having the radiating strire of the exterior rather distmctly 

 imj)ressed through, as it were, in consequence of the thinness of 

 the shell, and finely granidar, the granules being apparently con- 

 nected wdth the punctate structiu-e of the shell. 



Ventral valve compressed convex, the greatest convexity being near, 

 or a little behind, the middle, along a more or less prominent unde- 

 fined ridge, that sometimes, but not always, imparts a subcariuate 

 appearance to the central and umbonal regions; beak small, projecting 

 somewhat beyond that of the other valve, abruptly pointed, and rather 

 distinctly arched, but not strongly incurved; area about twice as 

 high as that of the other valve, and with its sharply defined edges 

 sloping to the lateral extremities of the hinge, directed and arched* 

 obliquely backw^ard with the beak ; foramen having near the form of 

 an equilateral triangle, but rather narrow^ed upward to the apex of 

 the beak, and partly occupied by the cardinal process of the other 

 valve. Interior showing the teeth to be moderately prominent; con- 

 cavity for the muscular impressions very shalloAV, small, somewhat 

 bifid anteriorly, and not defined by a very distinct margmal ridge ; 

 scars of divaricator muscles apparently narrow, and situated on each 

 side of a shallow mesial depression, which seems to include, far back 

 at its posterior end, those of the very small adductors, merely separated 

 from each other by a hairline ; impressions of ventral adductor muscles 



