THE NATURAL HISTORY SURVEY. 253 



Habitat: Same as costata. 



Remarks: This species is very rare. It may be distin- 

 guished from costata by its smaller size, wider umbilicus, and 

 by the last whorl being straight, while it is descending in cos- 

 tata. It is extremely local, and the only specimens found 

 were from one locality on the Du Page Feeder. It is by some 

 considered a synonym of costata, but seems to be sufficiently 

 distinct. 



SUBORDER BASOMMATOPHORA. 



"Tentacles flattened-triangular or subcylindrical, contrac- 

 tile (but not invertible); eyes at their bases, sessile." 



Shell usually covered by a corneous epidermis and oblong, 

 few whorled, without operculum. Mostly aquatic or littoral."* 



Superfamily Qehydrophila. 



"Teguments rugose; terrestrial, but usually inhabiting sea- 

 shores" (or bodies of fresh water).* 



FAMILY AURICULIDvE. 



"Shell spiral, covered by an epidermis, solid, usually thick; 

 spire more or less elevated; whorls sometimes flattened; aper- 

 ture elongated, contracted by columella teeth, and often also 

 by teeth within the lips." 



"Lingual membrane broad and elongated; teeth numerous, 

 in slightly bent cross-series; central tooth equilateral, narrow, 

 tricuspid; lateral and marginal teeth also tricuspid, rather ine- 

 quilateral, diminishing in size toward the outer edge. Head 

 ending in a snout; mouth with a horny, lunate upper jaw, and 

 with two dilated buccal lobes, united above, separate below; 

 tentacles subcylindrical, contractile; eyes sessile at the inner 

 sides of their bases. Mantle closed, with a thickened margin; 

 respiratory orifice posterior, on the right side. Sexes united."* 



Animal frequenting salt marshes or fresh bodies of water 

 (inland). 



GENUS CARYCHIUM Muller, 1774. 



Shell: Thin, few whorled, pupiform; columella armed 

 with a fold (sometimes absent); parietal wall armed with one or 

 two denticles; peristome expanded, with a denticle on the in- 

 side. 



*Tryon, Syst. and Struct. Conch., Vol. Ill, p. 92. 



