THE NATURAL HISTORY SURVEY. 341 



two; intermediate tooth similar to that of integer, excepting 

 that the perforation has a little lid or door which hangs below 

 the base of attachment; lateral teeth as usual, with about 

 twelve denticles, those of the first tooth larger than those of the 

 second (Fig. 124). (Stimpson.) 



Distribution: Ohio Valley; Ohio to Iowa, Michigan and 

 Wisconsin south to Kentucky. 



Geological distribution: Pleistocene. 



Habitat: Found in small ponds, ditches, eloughs and riv- 

 ers where there is a muddy or clay bottom. 



Remarks: This is the largest species of the genus found 

 in the area under consideration; this fact, together with its 

 subglobose form, will distinguish it. It is three or four times 



FIG. 124. 



Radula of SOMATOGYRUS SUBGLOBOSUS Say. (Stimpson, Hydrobiinae, 

 Fig. 14.) C, central tooth; 1, intermediate teeth; 2, 3, lateral teeth. 



the size of 5. integer. Subglobosus is fairly common and has 

 been found by Messrs. Ferriss and Jensen, the former at Joliet 

 and the latter on the lake shore and in George Lake. The 

 animal has not been observed. The spire of the shell varies 

 considerably in height, some being much more elevated than 

 shown in the figure. 



It has been found fossil by Mr. Jensen in sand banks on 

 the lake shore north of Graceland avenue. 

 140. Somatogyrus integer Say, pi. xxvi, fig. 2. 



Melania Integra SAY, New Harm. Diss., Vol. II, p. 276, 1840. 



Amnicola depressa TRYON, Proc. Phil. Acad., p. 452, 1862. (Variety.) 



Shell: Orbicular, solid, depressed; color subhyaline, some- 

 times inclining to dark horn; surface shining, lines of growth 

 oblique, fine, numerous, crowded, somewhat raised; sutures 

 rather deeply impressed; apex small, rounded; aperture roundly 

 ovate, somewhat produced at the lower part, subhyaline in- 

 side; spire short, rounded; whoVls four, convex, the last swol- 



