324 



THE CHICAGO ACADEMY OF SCIENCES. 



eral has seven to nine cusps, all large,' and the outer lateral has 

 eleven small cusps. All the teeth seemed to have well devel- 

 oped cutting points (Fig. 115, Mus. no. 12770). 



Genitalia: Not examined, but external appearance as in 

 subulare. 



Distribution: Lake Michigan, Ohio, Indiana, Illinois, Ken- 

 tucky, Tennessee. 



Geological distribution : Pleistocene; Loess. 



Habitat: Found in rivers and ponds, in more or less clear 

 water, on a sandy bottom. Does not like a muddy habitat. 



Remarks: This species is distinguished from subulare by 

 its very pronounced peripheral carina and flat-sided whorls. It 



n 



FIG. 115. 



Radula of PLEUROCERA ELEVATUM Say. 

 tooth; 1, intermediate tooth; 2, 3, lateral teeth. 



(Original.) C, central 



also attains a much larger size. When browsing on the glass 

 side of an aquarium, elevatum thrusts out its rostrum to its full- 

 est length, the tentacles are drooped and it slowly proceeds 

 in this manner, the radula being plainly seen in action at the 

 end of the rostrum. This species does not seem to be as com- 

 mon in individuals as subulare. It has been found fossil in a 

 cellar on the corner of Sheffield and Lincoln avenues. 

 1313. Pleurocera elevatum lewisii Lea, pi. xxxv, figs. 5-6. 

 Trypanostoma Lewisii LEA, Proc. Phil. Acad., p. 172, 1862. 



Shell: Differing from the typical form in being strongly 

 striate, the striae being raised into heavy ridges. The form is 

 also heavily banded with brown, and the satures are strongly 

 impressed. 



Length, 27.50; width, 10.00; aperture length, 8.00; width, 5.00 mill. (8745.) 



27.00; " 9.00; " " 8.00; " 4.50 " (8745.) 



39.00; " 15.00; " " 12.50; " 7.50 " (12312.) 



27.00; " 13.00; " " 11.00; " 6.00 '" (12312.) 



