24 THE NAUTILUS. 



anterior end, about two-thirds the length of the entire shell; peris- 

 tome thin, thickened within the aperture by 

 a heavy white or yellowish eallus, which 

 shows through the shell very plainly ; it i s 

 never bordered by any color stripe; the 

 callus of two or three former peristomes may 

 always be seen on the body whorl and some- 

 times one or two on the spire ; columella 

 broad, flat, white, a callus spreading over the parietal wall. 



Length 12.00 ; width 8.00 ; aperture length 7.50 ; width 3.00 mill. 



Length 10.50 ; width 7.50 ; aperture length 7.50 ; width 3.50 mill. 



Length 10.00 ; width 6.00 ; aperture length 5.50 ; width 3.00 mill. 



Animal not differing essentially from gyrina. Jaw similar to that 

 of gyrina. Radula similar in form to that of gyrina, but differing in 

 having six large, nearly equal cusps, instead of five, in the absence, 

 generally, of small cusps between the larger ones, and in the reflec- 

 tion being wider than in gyrina or heterostropha. The radula of this 

 species is remarkably uniform in the form of the teeth and in the 

 number of the cusps. The central tooth and secondary teeth 

 appeared to be the same as in the species previously described. 



Distribution : Great Lakes and St. Lawrence River, New r York, 

 Indiana, Illinois, Tennessee, Michigan, Wisconsin. Found in great 

 abundance in Allen's Creek, near Rochester, New York. Geologi- 

 cal distribution : Pleistocene ; Loess. Habitat : At stations similar 

 to gyrina. 



Remarks : This species has been generally confounded with heter- 

 ostropha, but will at once lie separated from that species by the spiral 

 lines ; the general form also is different from any other shell found 

 in this area, and the white callus on the lip is peculiar. It is a com- 

 mon shell at Hickory Creek, Lockport and Joliet, and has been 

 found, though more sparingly, at Calumet Grove, Maywood and at 

 Edgewater. It is more common than sayii, but less so than gyrina. 

 The specimens from Hickory Creek are quite typical, resembling 

 closely Haldeman's figures (pi. 4, figs. 7, 8) in his monograph of 

 fresh water mollusca. 



