286 THE CHICAGO ACADEMY OF SCIENCES. 



that this is true and that the typical American forms should be 

 called var. appressa, as distinguished by Say years ago. 

 Subfamily Planorbinae. 



"Lateral jaws present," "Tentacles filiform." "Foot short." 

 (Ball.) Genitalia on the right or left side. 



GENUS PLANORBIS Guettard, 1756. 



Shell: Dextral or sinistral, discoidal, with a flat, depressed 

 spire which is visible from both sides; aperture crescent shaped 

 or oval; peristome thin, simple, more or less expanded. 



Animal: (Fig. 94.) With a short, ovate foot; tentacles 

 slender, filiform, the eyes sessile at their inner bases; genitalia 

 on left or right side; lateral jaws present; radula with sub- 

 quadrate teeth, the central being bicuspid, the laterals tricuspid, 

 and the marginals serrated; ova deposited in a thin envelope. 



Genitalia: (Planorbis corneus, Bronn, Klassen und Ordnun- 

 gen der Weichthiere, taf. ciii, Fig. 10.) The ovotestis is long 



FIG. 94. 

 Animal of PLANORBIS. (Binney, Fig. 175.) 



and made up of a number of minute tubes; it is buried in the 

 liver, as in Limnaea; the ovisperm duct is very long, convoluted 

 at its upper part and terminates just below the albuminiparous 

 gland, which is rounded and made up of rather large cells; the 

 vas deferens is very long, thick at its upper part and narrow 

 at its lower part, and enters the penis near its summit; the 

 prostate is placed near the center of the vas deferens, and is 

 about three times as long as wide; the oviduct is rather long, 

 swollen at its lower part, where it enters the cylindropyriform 

 vagina; the receptaculum seminis is cylindrical, and its duct is 

 short and thick and enters the atrium near the female oriface 



(Fig- 95)- 



Distribution: World wide. 



KEY TO SPECIES OF PLANORBIS. 



A. Shell large, sinistral. 



a. Aperture not expanded. 



1. Apex sunk below the last whorl trivol-vis 



2. Apex flush with the last whorl truncatus 



