398 PROCEEDINGS OF THE ACADEMY OF 



H. tridentata, Say. la many of the specimens collected, the spire is 

 scarcely at all elevated, and in one or two the upper surface is quite plane. 

 Very common. 



H. labyrinthica, Say . 



H. chersi na, Say. I discovered a very large number of H. chersina and 

 labyrinthica in the old log previously alluded to. 



H. 1 i n e a t a, Say. 



H. a r b o r e a, Say. 



H. indentata, Say. 



Pupa armifera, Say. Exceedingly abundant. 



P. contract a, Say. Three specimens obtained. 



Bulimus margin atus, Say. Very numerous. The reflected lip is 

 larger in proportion than in Philadelphia specimens. 



No specimens of Snccinea were obtained. 



LlMNiEID^. 



Limnaea decidiosa, Say. I found some hundreds of this species on the 

 rocks at the junction of the Potomac and Shenandoah Rivers. 



L. colu m ell a, Say. Rather abundant. Specimens small size. 



L. catascopium, Say. Rare. Three or four obtained. 



Physa he t e r o strop ha, Say. One specimen. 



Planorbis 1 e n t u s, Say. One specimen found. 



P. trivolvis, Say. Numerous, but not attaining a large size. 



P. bicarinatus, S<iy. Very abundant ; much more so than the pre- 

 ceding species. The carina?, as in all the other fresh water mollusca from 

 this locality, are very prominent and sharp. 



P. parvus, Say. A few individuals were procured. 



P. e x a c u t u s, Say. Rare. Five or six only were found. 



Ancylus rivnlaris, Say. One specimen only, obtained from V. decisa, 

 to the body whorl of which it was attached. 



CONCHIFERA. 



Cyrenid^. 

 Sphserinm sulcatum, Lam. A very few specimens were found; the 

 rocky bed of the river being probably unfavorable to the multiplication of 

 bivalve shells. Those obtained possessed the same rugose epidermis which 

 seems to distinguish all the shells from this locality. 



Unionidje. 

 Unio cariosus, Say. This species attains a large size in the Potomac 

 River ; the individuals are not numerous, however, at Harper's Ferry. The 

 paucity of the Unionidce is remarkable in a region where the Gasteropoda, both 

 terrestrial and fluviatile. are so abundant. 



U. complanatus, Solander, (species. ) Valves very thin and shallow, 

 with the epidermis growing beyond their margins. The surface brilliant 

 green in the young shell, and brown in the adult. Not one specimen in ten 

 exhibits any green rays, even in young specimens. 



U. Fisherianus, Lea. Several good specimens taken. 



U. n a s u t u s, Say. This species, like U. complanatus, very seldom exhibits 

 a rayed surface. 



U. ochraceus, Say. A single individual obtained. 



[Dec. 



