20 BracMopoda of the Oincbmati Group. 



the extremity of which free, fleshy, spiral arms may, perhaps, have 

 been affixed. Under this shelly process, a longitudinal ridge separates 

 the quadruple impressions of the adductor, which on each side forms 

 two deep, oval depressions, placed obliquely one above the other, and 

 separated by lateral ridges branching from the central one; the 

 pallial vessels, as well as then- numerous minor bifurcations or veins, 

 have often left impressions within the ^valves; the principal trunks 

 seem both more numerous and better defined in the socket valve ; after 

 extending in a somewhat radiate or sub-parallel direction from the 

 muscular scars to near the anterior region, they sweep round sub- 

 marginally on both sides of the valve, leaving wide ovarian spaces 

 and giving off a series of smaller branches. 



OHkis testudmaria—(DAiMAi^, 1827). 



Suborbicular, plano-convex ; cardinal line straight, shorter than the 

 width of the shell ; ventral valve convex, much elevated toward 

 the beak, often with an elevated ridge down the center ; beak small, 

 slightly incurved; dorsal valve flat, or with a longitudinal depression 

 along the center, which often produces an emargination in front ; car- 

 dinal area small ; foramen small, triangular ; surface covered with fine 

 striiB, which bifurcate toward the margin, and are crossed by elevated, 

 thread-like lines, giving them a crenulated appearance. In the 

 interior of the dorsal valve the cardinal process is situated between 

 two small, projecting, deviating, brachial lamime, while the quadruple 

 muscular impressions are small, and divided into parts by a rather wide 

 mesial ridge. In the ventral valve the muscular area is moderately 

 developed, elongated, and forked in front. 



It is generally supposed to be common throughout the Cincinnati 

 Group, at all elevations, but forms usually classed with it in the lower 

 half of the group, now bear other names. Its range may, therefore, 

 be restricted to the upper part of the group, unless the midtiseda and 

 3Ieeki are regarded as varieties only. And, indeed, there is no form 

 found within the Cincinnati exposure that exactly agrees in the size 

 and situation of the muscular scars with the European specimens, and 

 it might be proper to class even the form that prevails in the upper 

 part, Avhich most resembles the type specimens of Europe, as a variety 

 under a distinct name. 



OHMs Meeki — (S. A. Miller). 



Shell small, plano-convex, rather depressed, transversely truncato- 

 suboval, the length being about five sixths its breadth ; hinge line, 



