THE NAUTILUS. 95 



Height at aperture, .80 ; greatest diameter, 2.75 mm, Cotype. 



Height at aperture, .80 ; greatest diameter, 2.50 mm. Cotype. 



Holotype, number Z 10772 and paratypes number Z 10773, 

 Museum of Natural History, University of Illinois. Cotypes 

 of urbanensis and altissimus have been placed in A. N. S. Phila. 



About 40 specimens of this form of parvus occur in the 

 marl collections taken from the University of Illinois campus. 

 The characteristics mentioned above appear to be very con- 

 stant and the race or variety of parvus seems distinguishable 

 enough for a distinct name. There were none of the parvus 

 form in the material. This may be a Pleistocene species that 

 has become extinct. Nothing similar has been seen in other 

 marl collections available for study, but it would seem that it 

 should be looked for in marl deposits, especially the older marl 

 beds overlying the earlier drift sheets, or in deposits between 

 these sheets interglacial. 



Planorbis altissimus n. sp. PI. VII, figs. 7-10. 



Shell depressed, with flatly rounded periphery 7 which is 

 placed below the center of the whorl; lines of growth fine, 

 crowded, but surface without spiral ornamentation ; whorls 

 4, regularly increasing in diameter, sloping flatly to the 

 rounded periphery; spire whorls sunken below the general 

 level of the surface, the whorls forming a rather sharp v- 

 shaped suture, causing the shell to resemble a miniature 

 Planorbis antrosus and producing a subacute cariua on the 

 upper surface of the whorls; base of shell deeply concave, 

 forming a wide, saucer-shaped depression and umbilicus; the 

 earlier whorls are carinate on the under side but the last 

 whorl is rounded ; the last half of the last whorl is markedly 

 deflected, forming a contact with but half of the preceding 

 whorl; aperture roundly ovate, shouldered above, the dorsal 

 margin much produced over the ventral margin, the parietal 

 callus joining the margins and causing the aperture to be 

 continuous. 



Height at aperture, 2.00; greatest diameter, 4.50 mm. 

 Holotype. 



