174* UNIVALVE SHELL8 



incrassated and heavy ; and although much decorti- 

 cated and eroded upon the spire, the tip is not trun- 

 cated. In the labrum also is a distinctive character ; 

 by comparison this part will be perceived to be less 

 arquated in its superior limb, than the corresponding 

 part in decisa. 



2. P. Hntegra. Shell olivaceous, pale, conic ; 

 whirls six, wrinkled across ; spire rather elongated, 

 entire at the apex ; suture profoundly indented ; 

 aperture sub-ovate, less than half of the length of the 

 shell. 



Inhabits the waters of the Missouri. 



Length 1-4 inch. 



Very much resembles P. decisa, the spire how- 

 ever is more elongated, and never truncated at the 

 apex, but always acute. 



3. P. *porata. Shell obtusely-conic or subglo- 

 bose; volutions four, convex, obsoletely wrinkled 

 across ; spire obtuse ; labrum and labium equally 

 rounded, meeting above in a sub- acute angle ; the 

 upper edge of the latter appressed to the preceding 

 whirl ; umbilicus very distinct. 



Inhabits Cayuga Lake. 



Cabinet of the Academy. 



This species which was found by Mr. Jessup, is 

 rather larger and more globose than P. limosa to 

 which it is allied, and has a more distinct umbilicus. 

 It resembles P. decipiens of Ferrussac, but is much 

 less acute, and rather smaller. 



