1889.] NATURAL SCIENCES OF PHILADELPHIA. 87 



thin, acute, continuous, but closely adnate on the parietal wall above 

 the sub-perforate umbilicus; columella slightly folded. 



Alt. 5-6, diam. 2 mill. 



Sumter Co. and Haulover Canal, at the head of Indian Kiver, Fla. 



This shell is similar to the form of B. nickliniana called B. atten- 

 uata Hald. in shape. It is distinguished by the low folds of the 

 surface. When these are well developed the shell has somewhat the 

 aspect of a tiny Goniobasis plicifera Lea. Mr. John Campbell of 

 Germantown, Pa., presented me with numerous specimens from the 

 locality last named. The apex is frecpiently eroded, as in most 

 Floridan fresh-water shells. The folds of the surface are a unique 

 character in American Bythinellre, but I do not doubt that 

 it belongs to this genus. I have seen specimens of Tryonia very 

 similar to the B. cequicostata, but usually Tryonia is more strongly 

 ribbed. I think it likely that this is the same form that was dredged 

 by Professor Heilprin in Lake Okeechobee* 

 Hydrobia monroensis FrauenfeM. pi. Ill, figs. 17, IS, 19. 



My attention was first called to Frauenfeld's descriptions of Flor- 

 idan Rissoidre when engaged in identifying a number of species 

 sent me by Mr. C.T.Simpson. About that time Dr. Dall published 

 descriptions of several Floridan Rissoids,f among them one which 

 he called Bythinella monroensis ; writing under it as a doubtful syn- 

 onym Hy. monroensis Frauenfeld. Upon looking over the Acad- 

 emy collection I found a specimen of H. monroensis marked by 

 Frauenfeld himself, and sent by him to Mr. Tryon many years ago. 

 This specimen is drawn in fig. 17 of pi. iii, and corresponds exactly 

 with Frauenfeld's description, which is as follows: 



" Eine Verwandte von jamaicensis Ad. oder cristallina [sic] Pfr. 

 durch mehr oder minder gerandete Naht unterschieden. Schale 

 keglich, nicht sehr stark, graugriin, cilglanzend. 5> Windungen, 

 leicht gewblbt, Naht gerandet. Mundung langlieh, nach unten stark 

 vorgaogen, oben ehoas gewinkelt, Saum nicht scharf, an der Windung 

 lang angelegt. Nabelspalte fein. Liinge 3.8 mill, Breite 2. 1 mill." 



All of Frauenfeld's specimens were from Lake Monroe. 



Note in this description the passages which I have italicized, and 

 which agree perfectly with the shells I have figured, but not at all 

 with Dr. Dall's species, which is quite a distinct form. 



*E.\plorations on the West Coast of Florida, ttc. Trans. Wagner Free Inst, i, 

 1887, p. 42. 



f Proc. U. S. Nat. Mus. viii, 1885, p. 256, el seq. 



