MIOCENE MOLLUSCA AND CRUSTACEA. 83 



extremity rounded; cardinal and lateral teeth very prominent and com- 

 pressed." (Conrad, in Miocene Foss.) 



A small fragment of the hinge part of a valve of what I consider as 

 this species has been obtained from the deep well-boring at Atlantic City, 

 N. J., and catalogued and cited by Prof. A. Heilprin as Mactra ponder osa f 

 From the compression of the beak and the thin and delicate shell and nar- 

 rowness of the teeth, as far as preserved, I do not think it can have belonged 

 to M. ponderosa ; it more nearly represents M. delumbis. Of course I can 

 only give my own individual impression. Still I think I am right in this 

 reference. There is not enough of the shell preserved to give a figure of, 

 so I have copied Mr. Conrad's figure from his Miocene Fossils. 



Genus PERISSODON Conrad. 



The first mention I find of this name by Mr. Conrad is its use for a sub- 

 genus under Rangia Desmoulins in his Catalogue of the Miocene Shells 

 of the Atlantic Slope, published in the Proceedings of the Academy of Nat- 

 ural Sciences of Philadelphia for 1862, p. 573, where he places under it 

 Gnathodon clathrodonta (G. Grayi of the Medial Tertiary Fossils) and Mactra 

 minor, Conrad. The name is placed at the head of the genus, but without any 

 reference to date or description, and no characters are given. It also occurs 

 in connection with the same two species in Meek's Check List of Miocene 

 Fossils, and also in Mr. Tryon's Structural and Systematic Conchology, as 

 a division under Rangia, though without characterization, but R. clathrodonta 

 Conrad is given as a typical form. It does not occur in any list or in any of 

 Mr. Conrad's subsequent writings, so far as I can ascertain after diligent 

 search, and is nowhere described. Considering Rangia clathrodonta Conrad 

 as the type, I can find no features on which to separate it from R. cuneata 

 of our southern coast. The anterior lateral tooth and pit may be said to be 

 proportionally smaller and the posterior ridge and groove more strongly 

 developed, and the entire shell thinner* and the hinge plate narrower, but 

 otherwise no difference appears. I shall use the name for the second species 

 mentioned (i?. minor), as it has been recognized by Mr. F. B. Meek and Mr, 

 Gr. W. Tryon, but do not consider it as a good division. 



