20 



VIVIPARA. 



Fig. 31. 



Paludina hicarinata, Potiez and Michaud, is certainly this 

 species, as shown by their description and the copy of the outline 

 of their figure given below. 

 Paludina bicarinata, Pot. et Mich. (1. c.) not Sat. — Shell oval, ven- 

 tricose, brown or greenish, covered with numerous trans- 

 verse ridges, two of which are more developed on the last 

 whirl, the other whirls having but one medial carina ; spire 

 comprised of three or four convex whirls, of which the first 

 are usually truncate ; aperture ovoid ; peristome simple. 

 Length 42-45, breadth of last whirl 10-12 mill. 



Mr. Say and Ch. des Moulins have both given the same 

 name to two different shells belonging to this genus, conse- 

 quently it becomes necessary, in order to avoid confusion, to change that 

 of Des Moulins, being posterior to Mr. Say's. Moreover, M. des Moulins' 

 shell having three carinae, will be better designated by the name tricarinata, 

 adopted in this catalogue. 



Delaware River, N. America. (^Potiez et Michaud.') 



Fig. 32. I give also an outline of Wood's figure (fig. 32) 



of decisa, of which no description is given, though it 

 is specified as "tawny Delaware." 



In addition to the above fac similes I have given 

 one of Say's figures in Nicholson's Encyclopedia (fig. 

 27.) 



§ 3. Shell sim2:)le. 

 a. Elongate ovate. 

 ViTipara poiiderosa, Say — Shell somewhat ventricose, much 

 thickened, olivaceous or blackish ; spire not 

 Fig. 33. much elongated, much shorter than the aper- 



ture, eroded at tip, but not truncated ; whirls 

 five, slightly wrinkled across ; suture pro- 

 foundly impressed ; aperture subovate, more 

 than half the length of the shell ; labium 

 with much calcareous deposit, and thickened 

 into a callosity at the su])erior angle ; within 

 tinged with blue. 

 Inhabits Ohio River. 



Greatest length, one inch and 11-20. Trans- 

 verse diameter one inch and 1-10. 



This shell is common at the falls of the 

 Ohio, and is a very remarkably thick and 

 ponderous species. It bears a striking resem- 

 blance to P. decisa, and has, without doubt, 

 Paludina ponderosa. been generally considered as the same ; but 



