SPH^NIA. 189 



There is no other painting or division of surface, neither is 

 there any carination of the umhonal ridge, which is by no 

 means strongly marked. The ventral margin is but mode- 

 rately convex, and neither peculiarly arcuated nor bulging 

 out either laterally or medially. The dorsal slopes are but 

 trifling, and almost equal to each other in declination ; the 

 front one is straight ; the hinder is slightly convex, but 

 chiefly so near its termination. Both extremities taper a 

 little ; the posterior is rounded, the anterior subangulated 

 above, but well rounded below. This subangulation is 

 more evident in the smaller valve. The umbones are not 

 prominent, and there is not the least appearance of a 

 lunule in front of them : the dorsal surface is, however, 

 rather depressed on both sides, but not peculiarly flattened 

 in either valve. The teeth are those of the section (or sub- 

 genus ?) Potamomya^ and appear identical with those of the 

 Corhula ustulata of Reeve (Conch. Iconica), to the young 

 of which species it altogether bears so remarkable a like- 

 ness, that we would not venture to assert its speciflc dis- 

 tinctiveness. The anterior subangulation is not, however, 

 there present, and the posterior termination has a slight 

 angularity at its lower extremity. The interior of ovata is 

 white, and rather dull. The breadth of the solitary ex- 

 ample (which does not aj^pear full grown, and is in a good 

 state of preservation) is one quarter of an inch, and its 

 lenoth is almost twice that measurement. 



SPH^NIA, TuRTON. 



Shell oblong, inequivalve, inequilateral, more or less 

 gaping anteriorly. Surface of the valve smooth or rugose, 

 covered with an epidermis. iJeaks incurved. Hinge com- 



