10 



its base numbers of dead sbells, which are found in all stages of preservation. 

 In some places, where well protected, these shells actually lay in heaps. In a 

 decayed log by the water side, neai-ly one hundred specimens of Helix and 

 Pupa were obtained. A close search on the hills on the north side of the Po- 

 tomac failed to discover a single species of Helix or Pupa. 



Helix al bolabris , Say. Diameter 1*25 inch. Spire rather depressed, 

 and aperture sub-triangular. Reflected lip very broad and flat, with a ten- 

 dency to form a tooth-like lamina near the umbilical region. Strhe coarse 

 aDd crowded. 



H. t h y r o i d e s, Say. A few specimens obtained. 



H. m o n o d o n, Rachett. This species appears to be rare at Harper's Ferry. 

 I found but one individual. 



H. hirsuta, Say. Common. All that were collected are entirely desti- 

 tute of the hairy epidermis. There is considerable difference in the convexity 

 of the upper surface, the spire being sometimes rather depressed. 



H. concava, Say. Dr. Binney, in his "Terrestrial Mollusks," states 

 that the upper and lower extremities of the lip are united in this species by a 

 thin callus on the columella. In the single specimen found by me, the callus 

 is very prominent. 



H. profunda, Say. Numerous. Attaining quite a large size, and with 

 close, narrow, raised stria?. But one brown revolving band is visible. 



H. pulchella, Mailer. Rare. 



H. tridentata, Say. In 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. c h e r s i n a, Say. I discovered a very large number of H. chersina and 

 labyrinthica in the old. log previously alluded to. 



H. lineata, Say. 



H. ar bore a, Say. 



H. indentata, Say. 



Pupa arm if era, Say.^ Exceedingly abundant. 



P. c o n t r a c t a, Say. Three specimens obtained. 



Bulimus marginatus, Say. Very numerous. The reflected lip is 

 larger in proportion than in Philadelphia specimens. 



No specimens of Succinea were obtained. 



Limn^eid.e. 



Limua?a decidiosa, Say. I found some hundred? of this species on the 

 rocks at the junction of the Potomac and Shenandoah Rivers. 



L. columella, Say. Rather abundant. Specimens small size. 



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



Physa heterostropha, 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, Say. Very abundant ; much more so than the pre- 

 ceding species. The carinse, 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. exacutus, Say. Rare. Five or six only were found. 



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

 to the body whorl of which it was attached. 



