296 THE CHICAGO ACADEMY OF SCIENCES. 



Habitat: Same as bicarinatus. 



Remarks: Campanulatus is distinguished from all other 

 Planorbes by its curious bell-shaped aperture. The flatness of 

 the whorls will also help to distinguish it. This species, like 

 bicarinatus^ is an inhabitant of rather deep water and it is diffi- 

 cult to obtain alive without a dredge. It is universally dis- 

 tributed throughout the area. The animal of campanulatus is 

 slow in movement and the shell is carried almost perpendicular. 



In studying the last four species the writer has noted that 

 there is considerable variation in the shape of the foot and 

 head. Bicarinatus has a long foot and a large, rounded head, 

 both flecked with white, and the tentacles are very long and 

 filiform; trivolvis has a broad, rounded, blackish foot, a wide 

 head and rather short, thick tentacles; in campamdatus the foot 

 is pointed behind and is very black; and in truncatus it is nar- 

 rower behind than before and is of a brownish color (see 

 Fig- 99)- If these four species be placed side by side these 

 differences may be plainly seen. 



SUBGENUS MENETUS H. and A. Adams, 1855. 



"Shell depressed, whorls rapidly increasing. Periphery 

 angulated." (Dall.) 



118. Planorbis exacutus Say, pi. xxvi, fig. 5. 



Planorbis exacutus SAY, Jour. Phil. Acad., Vol. II, p. 165, 1821. 

 Planorbis lens LEA, Trans. Amer. Phil. Soc., Vol. VI, p. 68, pi. xxiii, 



fig. 83, 1839. 

 Paludina hyalina LEA, Trans. Amer. Phil. Soc., Vol. VI, p. 17, pi. xxiii, 



fig. 81, 1839. (Monstrosity.) 

 Planorbis brogniartiana LEA, 1. c., Vol. IX, p. 24, 1844; Froc., Vol. II, 



p. 242, 1842. 

 Planorbis lenticularis LEA, 1. c., Vol. IX, p. 6, 1844. 



Shell: Dextral, very much depressed, with an acute per- 

 iphery; color pearly white; surface shining, slightly polished, 

 lines of growth numerous, oblique, slightly elevated; apex dis- 

 tinct, on a level with the spire; whorls four, rapidly increasing, 

 sloping in a well-rounded curve to the acutely keeled per- 

 iphery; spire very flat, all the whorls in the same plane, or 

 very slightly depressed at the apex; sutures impressed; base 

 of shell flatly convex; umbilicus rather narrow, deep, exhibit- 

 ing all the volutions; aperture obliquely ovate, sometimes 

 obtusely triangular; peristome thin, acute, the superior part 

 produced very much over the inferior part and expanded near 



