322 THE CHICAGO ACADEMY OF SCIENCES. 



tinct, but there is a total absence of copulatory organ in the 

 male. In the present species there is a peculiar sinus in the 

 female, on the right side of the foot, between the operculiger- 

 ous lobe and tentacle; the male is without this sinus. The 

 only way to be absolutely sure of the sexes is to crush the 

 body and examine with a microscope, when, if a male, sperma- 

 tozoa will be found, and, if a female, ova will be found. 



Distribution: New York to Great Lakes, south to Ohio 

 River drainage. 



Geological distribution : Pleistocene. 



Habitat: Found generally on a sandy or rocky bottom in 

 shallow water, where there is little or no current. 



Remarks: This species is subject to no little variation in 

 its obesity and ornamentation; the typical form is almost 

 smooth but the variety intensum is more strongly keeled on the 

 periphery and has several additional spiral lines. It is sepa- 

 rated from P. elevatum by its more rounded whorls, particularly 

 the last, and by its aperture, which is oval instead of triangu- 

 lar. The animal is slow and very sluggish in movement, and 

 in an aquarium spends most of the time on the bottom of the 

 tank, with its body half protruding from its shell and with its 

 rostrum and tentacles slowly moving about. The species 

 seems to be confined to the southern region and has thus far 

 been found only in Wolf Lake. 



1303. Pleurocera subulare intensum Anthony, pi. xxxv, fig. 3. 

 Melania intensum ANTHONY, REEVE, Monog. sp. 371. 



Shell: Differing from the typical form in being of a much 

 darker greenish-horn color, and in having the carina above the 

 suture extending in a more prominent manner to the base of 

 the last whorl. There are also seven subobsolete spiral lines, 

 especially on the base, which are not developed in subulare. 

 Length, 24.00; width, 8.00; aperture length, 7.00; width, 4.50 mill. (8735.) 



Animal, Dentition, etc.: As in subulare. 



Distribution and Habitat: As in subulare. (?) 



Remarks: The variety does not seem to be as common as 

 the typical form and has been found only in the Desplaines 

 River. It approaches elevatum in form, particularly when there 

 is a decided keel on the periphery. 



131. Pleurocera elevatum Say, pi. xxxv, fig. 4. 



Melania elevata SAY, Journ. Phil. Acad., Vol. II, p. 176, 1821. 

 Melania tracta ANTHONY, Proc. Bost. Soc. Nat. Hist., Vol. Ill, p. 361, 

 1850. 



