200 AMERICAN JOURNAL 



SPHiERELLA. 



Hinge of the right valve with three cardinal teeth, the two 

 anterior teeth small, entire ; posterior tooth rather elongated, 

 parallel with the hinge margin and slightly grooved. 



The above diagnoses shows a wide difference in this genus to 

 Diplodonta or Felania. The muscular impressions are larger 

 than those of the allied genera and the posterior cicatrix is 

 much nearer the ventral margin. The posterior tooth described 

 above may be said to coalesce with the adjacent tooth at the 

 base. The left valve has one small direct cardinal tooth under 

 the apex and an elongated, compressed, very oblique tooth, with 

 a pit between them. All the species are subsphgeroidal, and con- 

 stitute a group of rounded bivalves with a profounder cavity 

 than exists in any other genus. 



There is one species in the Miocene of Virginia, one in the 

 Oligocene at Vicksburg, and the recent Lucina orbcMa, Gould, is 

 a species of Sphcerella, in which the muscular impressions are 

 very large and unlike those in Diplodonta. 



S. SUBVEXA, Conrad. PI. 11, fig. 9. Hinge view. 



ANODONTA. 



A. DECURTATA, Conrad. PI. 11, fig. 8. 



Subtrapezoidal, inflated ; umbonal slope abruptly rounded or 

 subangular ; posterior are depressed, wide ; disk flattened medi- 

 ally ; umbo obtusely rounded ; posterior margin obliquely trun- 

 cated. 



Locality. Colorado. 



This description is from a cast in a yellow arenaceous rock. 



MELANIA, Lam. 



M. DECURSA, Conrad. PI. 13, fig. 5. 



Subulate, volutions 10 ? slightly convex, penultimate volution 

 sculptured with three distant, prominent, tuberculated, revolving 

 lines, and a minute line between the two lines towards the 

 suture ; last volution with seven lines, two of them large and 

 prominently tuberculated, ; aperture ovate. 



Locality. Accompanied the Anodonta, but the rock in which 

 it occurs is a mixture of sand and shell fragments, in which 

 many specimens of these shells are replaced by chalcedony. 



CARYATIS, Roemer. 

 Cytherea convexa, Say. 



This Miocene species must retain Say's name convexa, which 



