11 



CONCHIFERA. 



Cyrenidje. 



Spha?riuni s ul o a t u m , 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. 



Unionid;e. 



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 Unionid > is remarkable in a region where the Gasteropoda, both 

 terrestrial and fluviatile are so abundant. 



U. c o m p 1 a n a t u s , 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. Fisher ian us, Lea. Several good specimens taken. 



U. n as u tu s, Say. This species, like U. complanatus, very seldom exhibits 

 a rayed surface. 



U. o c h r a c e u s, Say. A single individual obtained. 



U. radiatus, Lam. Beautiful specimens occur on the Potomac, with a 

 light green polished epidermis, with broad dark rays, and frequently pencilled 

 rays in the intermediate spaces. 



Margaritana undulata, Say. (Sp.) Very rare. Nacre delicate pink, 

 epidermis in adult shells jet black, much eroded at the beaks. 



M. marginata, Say. (Sp.) I collected a number of specimens. They 

 were all of small size. Epidermis in the young shells elegantly rayed. 



Auodonta fluviatilis, Dillwyn.(B-p.) A few individuals were taken ; their 

 surface is almost a uniform dull brown, vastly inferior in beauty to those 

 from the vicinity of Philadelphia. 



A. i m p 1 i c a t a, Say. One specimen. 



A. e den tula, Say. One perfect young shell, and several larger odd 

 valves were taken ; they exhibit the same uniformity of color as A. fluviatilis. 



The above shells were all collected within the space of two hours, such was 

 their great abundance. A more prolonged search would doubtless add a few 

 more species to the list, particularly among the smaller terrestrial shells. The 

 Molluscous fauna of Harper's Ferry is distinguished for the development of 

 heavy lines of growth and acute prominent carinas on the shells of the spe- 

 cies ; and in the terrestrial shells, by the depression of the spire. It is strange 

 that a climate which has evidently exercised some influence on the growth of 

 the Mollusca, has still permitted a vast multiplication of individuals. 



