TO GEOLOGY. 91 



Observations. A single specimen (both valves) only 

 has come into my possession. Being somewhat worn, it 

 is difficult to say if the species be squamose or smooth. 

 The superior valve seems to be concentrically striate. On 

 the posterior edge of the upper valve there are a few 

 wrinkles. 



O. divaricata. Plate 3. Fig. 70. 



Description. Shell semi-lunate, somewhat convex, sub- 

 angular at dorsal margin and recurved, rounded at basal 

 margin, furnished with divaricate ribs over the whole sur- 

 face ; margin crenulate, raised before the beak. 



Diam Length 1.5, Breadth .8, of an inch. 



Observations. Like the last, it is difficult to make out 

 the characters from a single specimen. It has some re- 

 semblance to the O. costata (Sowerby), but is a larger shell 

 and not orbicular. 



O. Jllabamiensis. Plate 3. Fig. 71. 

 Two Views. 



Description. Shell subelliptical, curved behind, crenu- 

 late on both sides of the beak ; beaks recurved, pointed. 



Diam Length 2.1, Breadth 1.5, of an inch. 



Observations. A single valve only of this species has 

 been received by me. The exterior of this is roughly 

 squamose. 



