NATURAL SCIENCES OF PHILADELPHIA. 443 



Genus CALLISTA, Poli. 



Callista Deweyi. 

 Cytherca Deweyi, M. and H., 1856, Proceed. Acad. Nat. Sci , Pbila., p. 83. 

 Meretrix Deweyi, M. and H., 1860, " " " " p. 185. 



We have recently had an opportunity to examine some specimens of this 

 species, exhibiting the hinge and other internal characters which we had not 

 previously seen. These show that it cannot properly go into the genus Mere- 

 trix, (Cytherea,) as that group is now restricted by those conchologists who 

 take as its type such forms as M. impvdica, but that it possesses the 

 characters of Callista, Poli, (Dionc, Gray,) to which we now remove it.* 



The collections recently brought in from a locality on Deer Creek, a tribu- 

 tary of the North Branch of Platte River, contain a large number of specimens 

 apparently of the above species, in a fine state of preservation. Many of these 

 arc much larger than the original typical specimens from the Yellow Stone 

 and Moreau Rivers, and they all likewise differ in being a little less convex 

 and in having a somewhat narrower and deeper pallial sinus. It is possible 

 these Deer Creek specimens may belong to a distinct species, but they agree 

 in so many respects with' C. Deiveyi that we do not feel quite warranted in 

 separating them specifically. If they should prove distinct, however, we 

 would propose to designate them by the name C. robusta.f 



Genus TELLINA, Linnreus. 



Tellina nitidtjla. 



Shell transversely ovate, thin, rather short and convex for a species of this 

 irenus ; anterior side regularly rounded ; base semi-ovate, the most prominent 

 part being in advance of the middle : posterior side narrower than the other, 

 rounding down from above with a graceful, oblique curve; postero-basal ex- 

 tremity rather narrowly rounded and slightly bent to the right ; dorsal outline 

 sloping from the beaks at an angle of about 130 ; beaks moderately promi- 

 nent, approximate, located a little in advance of the middle ; posterior umbo- 

 nal slopes prominent from the beaks to the postero-basal extremity, but not 

 forming a distinct fold. Surface with fine concentric stria?, and a few stronger 

 marks of growth. Sinus of pallial line of moderate length, and directed 

 somewhat obliquely downwards ; posterior muscular impression broad ovate. 

 (Hinge unknown.) 



Length, (of a specimen a little under medium size,) 1-10 inches ; height, 0'82 

 inch; convexity, 0-40 inch. 



Not having seen the hinge of this species, we cannot determine with positive 

 certainty its generic characters, though it has the habit and general aspect 

 of a Tellina. It is worthy of note, however, that the sinus of its pallial line 

 seems to be rather short for a species of that genus. In form it resembles 

 somewhat closely our Tellina? Cheyennensis, (Proceed. Acad. Nat. Sci., Phila., 

 Apr., 1856, p. 82,) but is a thicker shell, with more pointed beaks, while its 

 concentric striae are not near so regularly arranged. 



Locality and position. Same as preceding. 



Genus LINGULA, Bruguiere. 



LlNGULA NITIDA. 



Shell small, extremely thin, narrow subelliptical in outline, the greatest 

 breadth being near the middle ; front very narrowly rounded ; sides forming 



* Our Cytherea Owevana, (Proceed. Acad. Nat. Sci., November, 1856,) and C. orbicu- 

 lata, Hall arid Meek, should probably also br removed to the same group. 



t Since ihis was in type, farther comparisons have satisfied us that this is distinct 

 from C. Deweyi, and we now adopt for it the name Callista robusta. 



1861.] 



