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 Planorbine. 
“Lateral jaws present,” “Tentacles filiform.” ‘‘Foot short.” 
( Dall.) 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. 
Gentalia: (Planorbis corneus, Bronn, Klassen und Ordnun- 
gen der Weichthiere, taf. ciii, Fig. 10.) The ovotestis is long 
Fie. 94. 
Animal of PLANORBIS. (Binney, Fig. 175.) 
and made up of a number of minute tubes; it is buried in the 
liver, as in Limnza; 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...................... trivolvts 
2. Apex flush with the last whorl....................55- truncatus 
