122 



LAND AND FRESII-WATER SHELLS OF N. A. [fART TI. 



Fig. 202. 



two ; left side truncated, presentiug a flat surface extending across all the 

 Avhirls, the suture being marked by a minute raised line, which lik.wise 

 extends around the edge of the truncation; tin space 

 between the volutions of this raised line, as well as the 

 entire body of the shell, is beautifully marked with deli- 

 cate longitudinal lines, which are crossed by the minute, 

 raised, transverse lines of growth ; whirls on left side 

 four or five ; aperture ovate, widest on the right side, 

 whi(!li extends beyond the general plane of that side of 

 the shell ; the lip on the left side is straight for a short 

 distance from the body whirl, and to a line with the truncated plane, at 

 the outer edge of which it forms an angle, marked on the inner surface 

 by a slight groove, corresponding in the raised line separating the whirls 

 on the outside ; lip thin, slightly thickened by a bluish white callus, 

 bordered on the inner edge by a purplish band ; the longitudinal lines, 

 as well as the transverse lines of growth, are distinctly seen within the 

 aperture. Measurements, 6 — 35. 

 Ilah. Saginaw Bay. 



In a few specimens the growth of the whirls has not been in the same 

 plane, leaving a slightly projecting turreted spire on the left side. (J///es.) 



Planorbis truncatus, MiLES in Winchel's Geol. Surv. Michigan, 1861, p. 238. 



Fig. 202 is drawn from No. 9010 of the collection, furnished 

 by Prof Miles, whose description is given above. 



Fig. 203. 



PlailorlJis fragilis, Duxker. — Shell tumid, fragile, very delicately 

 striate, pale horn or amber colored ; deeply umbilicate above, 

 below rather concave; wliirls four, involute, on each side 

 rounded, rapidly increasing ; the upper ones spimlly 

 striated and decussated, conspicuous below ; aperture large, 

 spreading, oblique, kidney-shaped ; lip very acute, with a 

 very delicate, white callus on the parietal wall. 



Shell very ventricose, very thin and fragile, delicately 

 striated, pale horn or amber colored ; above very deeply 

 umbilicated, with the apex hardly visible ; below, slightly 

 concave. Whirls four, rounded, strongly involute and 

 rapidly increasing, the last with microscopic strise ; aper- 

 ture oblique, wide, kidney-shaped ; on the parietal wall is 



a delicate callus connecting the termini of the peritreme. 

 Planorbis ^ 



fragilis Greatest diam. .6, height at aperture 3^ lines. 



03 



