North American Helicidce. 89 



Tlie following are measurements of large and small specimens 

 in my cabinet : — 



Diam, maj. 14, min. 12| mill, Alt 3 mill. anf. 8|- 



Associated with septemvolva, Mr. Dorman found not only the 

 shell described by Pfeifier as JI. volvoxis, but an intermediate 

 form, in which the flat upper surface and carina of the former, 

 are combined with the more tumid character, and breadth of 

 the last whorl beneath of the latter. In many specimens the 

 uniform opaque light color of the base of each whorl is a 

 striking feature. Mr. Dorman informs me that in some places 

 in St. Augustine the three forms are found together, but that 

 septemvolva and volvoxis generally inhabit different localities. 



Helix volvoxis Parreyss, 



Pfeiffer's description of this species is as follows : — 



T. umbilicata, orbiculato-convexa, tenuis, rufo-coniea, pellucida, regu- 

 lariter costulato-striata ; spira brevissima, convexa; anfr. *J convexi, 

 regulariter accreseejites, ultimus reliquis superne vix latior, .-angulatus^ 

 infra angulum inflatus, striatus, nitidus; iiinbilicus latus, regularis, 

 anfractu ultimo latissimo, reliquis regulariter decrescentibus ; apertura 

 majuscula, reniformis ; perist. intus callosum, reflexuui, marginibus callo 

 brevi, triangulari, dentiformi junctis. Diam. maj. 9, min. 8; Alt. 4, mill. 

 Habitat in America boreali : Georgia, Florida. 



Obs. Ilanc speciem, a pr»cedente (H. ccreolus Miibl.) toto coelo diver- 

 sam, saepius ex America nomine II. septemvolviE Say accepimus. 



This shell is very generally labelled in cabinets H. septem- 

 volva, but I entertain great doubts, looking at my extensive 

 suite of specimens, as to its specific difference. 



The form described by Pfeiffer is common in St. Simon's 

 Island, Ga., whence I have examples collected by Mr, Postell. 



It varies in size, — the following are the measurements of a 

 small specimen, having 6^ whorls : — 



Diam. maj. 74, min. 6i ; Alt 3 mill. 



