90 PALEONTOLOGY OF OHIO. 



There may be some doubt as to the true generic relations of this 

 species, as the specimen does not present any of the internal features. 

 It can not with propriety be placed under Modiolopsis or Orthodesma, as 

 the projecting beaks is a feature not likely to pertain in a species of 

 either of those genera ; we therefore place it provisionally under the 

 genus Sedgwichia, from a resemblance in external form to some of the 

 species referred to that genus by its author, although we are in great 

 doubt as to the precise characters of that genus, from the heterogeneous 

 material referred to it. 



Formation and locality: In the shales of the Hudson River group, at Blanchester, 

 Ohio. The specimen described and illustrated is the property of U. P. James, Esq., 

 of Cincinnati, and is, we believe, the only individual yet discovered. 



Genus CUISrEAMYA (new geu.). 



Thin, fragile, bivalve shells, with ventricose valves, and strong, prom- 

 inent, incurved beaks. Cardinal line straight, or gently curved. Hinge 

 edentulous. Valves united by an external ligament of greater or less ex- 

 tent, posterior to which the margins of the valves overlap each other to 

 the extent of the cardinal line. Margins of the valves inflected along 

 the cardinal border, forming a narrow escutcheon posterior to the beaks, 

 and anteriorly a well-defined lunule is situated below the beaks. Ad- 

 ductor muscles, at least two, are anterior and posterior. Pallial line sim- 

 ple. Type, Cuneamya Miamiensis. 



The above genus is proposed for the reception of a group of Silurian 

 Lamellibranchiate shells, which have been variousl}^ referred to Lepto- 

 domus, Grammysia, Sedgwichia, etc., but which do not appear to us to 

 possess the true features of any of those groups ; and although the entire 

 features of the shells under consideration have not been fully and posi- 

 tively determined, the want of a term by which to designate them is so 

 strongly felt in their description that we have thought it advisable to 

 propose a group for their reception, rather than to refer them to one with 

 which we are perfectly satisfied they have no affinity. Although Prof. 

 McCoy has himself described similar forms as Leptodomus, yet the type 

 of that genus is of such an entirely different nature that we do not hesi- 

 tate to pronounce these as belonging to an entirely different class of 

 shells. From Grammysia they differ considerably in their external char- 

 acters, but more decidedly in the absence of the strong, tooth-like fold of 

 the hinge, which the shells of that genus are now known to possess. 



