Bmchiojwda of the Cincinnati Group. 25 



and proceeded to redefine it. And here he made another singular 

 mistake ; in his quotation from Prof. Hall's definition, he says : "lam 

 in considerable doubt whether it was this or the following form 

 to which Prof Hall applied the nanfe 0. emacerata. His remark, 

 that his type has finer stri^, and the depression in the middle of its 

 dorsal valve usually deeper, and the mesial elevation of the ventral 

 valve more prominent than in the form most generally referred to, 

 0. tedudinaria, would seem to indicate that he had the following form 

 in view, and regarded that here under consideration as the 0. 

 tedudinaria." 



It will be observed that Prof Hall said just the reverse of what is 

 here ascribed to him. He said : " The depression in the center of the 

 dorsal valve, and elevation in the the center of the ventral valve, are 

 less conspicuous, and the hinge line proportionally longer, generally, 

 than in 0. tedudinaria." 



With hicorrect information, and through inadvertence, Prof Meek 

 has well defined and illustrated a form (heretofore generally identified 

 as 0. tedudinaria) as typical of Hall's species emacerata, but which I 

 regard as distinct from both, and certainly far removed from the 

 emacerata. I have called the form described and pointed out by Prof. 

 Meek, 0. Meeki, and it matters but little whether it is regarded as a 

 variety of tedudinaria, or as a distinct species, because it is at least a 

 form that may be generally recognized. 



The 0. emacerata may be farther distinguished, as follows : It is larger 

 than the 0. multisecta, with which ;t is associated ; its valves are thin- 

 ner, strire finer, greatest convexity nearer the beak, and nearer semi- 

 elliptical in form ; the muscular impressions on the dorsal valve are 

 larger in proportion to the size of the shell, differ a little in shape, 

 being irregular, sub-trapezoidal in outline, and the cardinal process 

 is more distinctly trifid ; the muscular impressions on the ventral valve 

 are wider, and better defined, with proportionally a much stronger in- 

 dentation on the sides at the line of separation of the scars. It may be 

 further remarked, that there is no graduating of the shells called 

 multisecta into this form, so far as observed, though they are abundant 

 in the same rocks, and above and below them. 



OHhis lynx — (Von Buch, 1837). 



Shell attaining a large size, nearly equivalve, wider than long, 

 with a transversely oval, subquadrate outline, or, in old specimens, often 

 becoming so gibbous as to assume a subglobose form ; hinge line either 

 a little less or exceeding the greatest breadth of the shells ; cardinal 



