UNlOKIDiE FKOM THE CAMDP::^[ CLAYS. 245 



anterior third of the length. Surface of shell smooth, valves compressed 

 and subangular along the umbonal ridge. Muscular scars strong on the 

 anterior end, and rather faintly marked on the posterior sides; lateral teeth 

 strong, of great length, and nearly or qurte straight, cardinal teeth propor- 

 tionately small and strongly striated. 



Mr. Lea remarks of this species that it *4s very nearly the same in 

 outline with the well-known nasuUis Say, but is more acute at the pos- 

 terior margin, in which character it is more nearly allied to Fisherianus.^^ 

 There is certainly a very close resemblance between these fossil forms and 

 the ordinary forms of Z7. nasutus, as they occur in the Hudson River and 

 its confluents, especially those from the Mohawk and those from the Erie 

 Canal in its eastern parts. Some of the shells which I have seen of this 

 species preserve the form very perfectly, though much of the shell substance 

 has been removed, especially along the hinge. The lateral teeth appear to 

 have been very strong, and the cardinal ones are longitudinally striate 

 more strongly than any I remember to have seen in U. nasutiis ; but the 

 shells have been considerably thickened, as is evidenced by the strong 

 anterior muscular scars. The epidermis has also been strongly ridged. 

 Among the specimens loaned me by Prof H. C. Lewis I find one specimen 

 which is more broadly truncate posteriorly- and would seem to have had a 

 much greater thickness, especially behind the middle of the valve. This 

 one I have been somewhat inclined to place under U. prceanodontoides 

 described for the first time, but it lacks the cylindrical form, although 

 partially possessing the oblique median sulcus of that one. 



Unio radiatoides. 

 Plate XXXIV, Figs. 1-3. 



Unio radiatoides Lea. Proc. A. N. Sci., Pliil., 1868, p. 163. Pamphlet by I. Lea, p. 30. 



Shell of moderate size, transversely broad-oval in outline with com- 

 pressed or gently convex valves, generally a little narrower at the anterior 

 than at the posterior end; the hinge-line gently arcuate and slightly rising 

 posteriorly. Shell surface marked by concentric lines of growth. Anterior 

 muscular scar large, round; posterior scar faint. Cardinal teeth compara- 



