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 ponderosa ? 
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. 
} g 
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 Miocené 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 
Grnathodon 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, 1 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. | shall use the name for the second species 
mentioned (R. minor), as it has been recognized by Mr. F. B. Meek and Mr, 
G. W. Tryon, but do not consider it as a good division. 
