NATURAL SCIENCES OF PHILADELPHIA. 57 



Length of largest specimen, 0-34 inch; height, 0-30 inch; convexity, 28 

 inch. 



The most marked characteristics of this species, are its quadrato-suborbic- 

 ular, rather gibbous form, very nearly central beaks, and particularly its 

 sharply elevated concentric striae, growing stronger, more prominent" and 

 more distantly separated on the umbones, until near the points of the same 

 they often assume the character of sharp, raised plications. In some of the 

 smaller specimens, these raised, rather distantly separated, stronger strue, ex- 

 tend over nearly the whole surface; while in others they pass gradually into 

 mere irregular lines of growth, on most of the surface, occasionally separated 

 by wider furrows. 



In form this species is very similar to the existing S. Vermontanum, of Prime, 

 with which it also agrees nearly in size. It is more regularly rounded in 

 front, however, and has stouter lateral teeth ; while its concentric raised 

 atrias and sulcations are generally larger and grow more distinct on the um- 

 bones than below, instead of the reverse. In this latter character of marking 

 it agrees more nearly with S. aureum, Prime, from which, however, it differs 

 entirely in form. 



Locality and position. Hot Spring Mountains, at Fossil Hill, Idaho Terri- 

 tory. 



Sph.eriom? Idahoense, Meek. 



Shell attaining a very large size, moderately convex, rather thick in propor- 

 tion to size ; orbicular-subovate in outline, being wider in front than posteri- 

 orly ; anterior margin regularly rounded ; base semioval in outline ; posterior 

 margin somewhat narrowly rounded below and sloping forward above ; dorsal 

 margin short. Beaks placed in advance of the middle, a little compressed 

 and directed obliquely forward and inward. Surface marked by concentric 

 6tria; and furrows. Later teeth stout. 



Length, Q'98 inch ; height, about 92 inch ; convexity, about 0-54 inch. 



The specimens of this shell are not in a very good state of preservation, 

 being, with oue exception, internal casts, and this one only retains a part of 

 the shell. They certainly differ, however, from the last not only in their much 

 larger size, but in being less nearly equilateral, more produced, and rather 

 more narrowly rounded posteriorly, as well as proportionally less convex. 

 The internal casts have the umboual region, from a little above the middle 

 of the valves, compressed. Some of these casts show a few rather distinct, 

 broad, irregular concentric undulations, that were doubtless more strongly- 

 defined on the exterior of the valves. 



None of the specimens of this shell show the hinge very clearly, but from 

 its large size and thickness I was at first inclined to believe it a Cyrena or a 

 Corbicula. Impressions in the matrix, however, show that its lateral teeth are 

 not striated, nor of the form seen in the latter genus. Possibly, I should call 

 it Cyrena Idahoemis. As its pallial line is certainly simple, however, and not 

 sinuous, as in all the American living species, and, so far as known, in all the 

 fossil Cyrenas and Corbiculas of this continent, I have concluded to place it 

 provisionally in the genus Sphoerium, until better specimens can be obtained 

 for study. 



Locality and position. Same as last, and from same formation at Castle 

 Creek, Idaho. 



Ancylus cndulatus, Meek. 



Shell thin, attaining a very large size, elliptic-oval in outline, being some- 

 times slightly widest a little in advance of the middle; apex much elevated, 

 pointed, curved backward and placed about half-way between the middle and 

 the posterior margin ; posterior slope concave ; lateral slopes nearly straight ; 

 anterior slope distinctly convex. Surface marked with fine, rather obscure 



1870.] 



