38 PALEONTOLOGY OF NEW JEKSEY. 



and somewhat flattened area, not very unlike that of an oyster, marked 

 throughout its length by a median parallel groove and ridge. The other 

 has a much smaller area, but possesses the groove and ridge in a modified 

 form. The shells are very much thickened, in which feature they differ 

 greatly from most of the mytiloid forms. The muscular system, so far as 

 I have been able to observe it, is like that of Mytilus; consequently the 

 stability of the genus rests entirely on the great thickness of the shell and 

 the peculiar hinge area; but these are so very marked that they cannot 

 well be misunderstood, and the genus appears to be a valid one. 



Mytiloconcha incrassata. 

 Plate V, figs. 10 and 11, and PI. vi, figs. 1 and 2. 



Mytilus incrassatus Conrad: Am. Jour. Sci., vol. 41, p. 347; Mioc. Foss., p. 74, PL xlii, 

 fig. 4; Heilprin: Proc. Acad. ^Nat. Sci., Phil., 1887, p. 402; Tuomey and Holmes: 

 Plioc. Foss., S. P., p. 32, PI. xiv, figs. 1 and 2; Emmons' Geol., N. C, p. 283, fig. 

 203a. 



Mytiloconcha incrassata Conrad: Proc. Acad. Nat. Sci., 1862, pp. 290 and 579; Meek: 

 Check List Mioc. Foss., 7. 



u Thick, much inflated; anterior margin slightly incurved above the 

 middle; hinge thick with slightly prominent robust teeth." (Conrad.) 



I have seen only the apical portions of valves of this species among 

 the New Jersey collections. The shells have apparently been of moderate 

 size, but the outer parts have scaled off from the inner layers, leaving only 

 a very small part of the valves with a portion of the hinge-plate preserved; 

 they show, however, the curvature of the shell and the characteristics of 

 the hinge sufficiently well to identify them as of this species rather than of 

 M. incurva, as the ribs forming the teeth are continued on the inner part of 

 the hinge-plate, and the external parts are covered by the callus and 

 rounded — quite different from the flattened and grooved plate of M. incurva. 

 I have figured an example from South Carolina to aid in the identification 

 of other specimens. 



Locality: Those which I have for use are from Shiloh, N. J., and are 

 from the collection of the National Museum. The larger specimen figured 

 from South Carolina is from the American Museum of Natural History. 



