296 littorinidj:. 



to New York, and from Missouri to Michigan. It is also found in 

 the postpleiocene of the Mississippi River bluffs. 

 Housatonic River {himleif). 



Family LITTORINIDiE, Gkay. 



Shell spiral, turbinated or depressed ; aperture simple in front, 

 never pearly within. 



Ociiiis SKEIVEA, Fleming. 1828. 



Shell minute, discoidal ; whorls few, and destitute of spines ; 

 aperture dilated ; operculum horny. 



Skenea planorbis. 



Fig. 189. 



Shell minute, discoidal, concavely umbilicatod beneath, horn colored, whorls 

 three, mouth expanded. 



Turbo planorbis, 0. Fabricius, F.iiina Gr. 394. 



Skenea jilanorbis, Forbks and IIanley, &e. ; Stimpson, Shells of New England, 35 ; 



Check Lists, 4. 

 Skenea serpidouhs, of American not European authors, Gould, Inv. Istcd. p. 247, fig. 189. 



Shell minute, flat, slightly convex above, and broadly concave be- 

 low, forming a deep umbilicus, which displays all the whorls within ; 

 whorls three, smooth, a little depressed, light horn color ; 

 Fig 563. jjpg^ scarcely elevated ; suture channelled ; aperture turn- 

 ing downwards, circular, somewhat trumpet-shaped, in con- 

 tact with, but not embracing any part of, the preceding 

 whorl ; lip sharp, and receding so as to form an acute gap 

 ^ofb?J^' ^^ ^^ joins the preceding whorl ; operculum horny, multi- 

 spiral, the apex central. Breadth, one twentieth of an inch ; 

 height, one thirtieth of an inch. 



Clings to stones lying about low-water mark. I have found it 

 occasionally, but Professor Adams lias found it in great numl)ers 

 along iha southwestern shore of East Boston. Nova Scotia ( Wil- 

 lis^ ; Cape Cod, northward (^Stimpson). 



Genus RISSOELLA, Gray. 1847. 



Shell thin, spiral, conical, or sub-globose, transparent ; aperture 

 ovate, rounded and simple in front, peristome thin, entire. 



