92 UNIVERSITY OF COLORADO STUDIES 



parietal teeth, i columellar, i basal, a long curved one within outer lip, 

 a long entering lamella curving from outer basal angle to behind columella, 

 peristome white, unreflected, imibihcus open, deep, height i . 4 mm., 

 width o . 9 mm. Vertigo milintn 



** Terrestrial Naked Slugs 



A. Unicolored, unspotted. Agriolimax campestris and var . 



B. Darker reticulated lines on lighter ground color giving a spotted appearance. 



Agriolimaz agrestis 

 *** Fresh-Water Snails 



A. Discoidal, whorls coiled in one plane. 



a. More than 5 mm. in width. 



1. Color white to brown, whorls 4, spire flat from above, depressed and showing 2 J 

 to 3 whorls from below, whorls slightly carinate above, width 15 to 20 mm. 



Planorbis trivolvis 



2. Distorted form of trivolvis, plane of inner whorls inclined to that of outer whorl 

 so that carina of 3d whorl forms a shoulder on right side and sinks beneath 

 outer whorl on left side. Planorbis plexata 



3. Whorls 3, sharply carinate above and below, conically depressed above and 

 below, smaller than trivolvis, V-shaped aperture extending above top of body 

 whorl. Planorbis bicarinatus 



b. Less than 5 mm. in width. 



1. Color bright horn to black, imibilicus vnde and shallow, showing all volutions 

 from above and below, apex depressed somewhat below top of last whorl. 



Planorbis parvus 



2. Whitish, with deeper, narrower umbilicus than parvus, apex not sunken. 



Planorbis tunbilicatellus 



3. Dark brown, periphery of outer whorl sharply carinate. 



Planorbis exacuous 



B. Small, depressed conical, patelliform. 



a. Fragile, sides parallel or incurved in middle, apex elevated and curved backwardt 

 I from anterior end of shell, extreme length 4 mm., width i . i mm., height 

 I mm., usually much smaller. Ancylus fragilis 



h. Similar to, if not identical with, fragilis. Ancylus caurinus 



c. Pale, thin, delicate, sides nearly straight, not quite parallel, apex sharp, f from 

 anterior end, turned to right. Ancylus parallelus 



C. Spire depressed, but apex raised considerably above body whorl, color brownish, shin- 

 ing, whorls 3i, last much deflected, making aperture nearly round and continuous, 

 peristome simple and nearly continuous, easily distinguished from all other Colorado 

 species. Valvata lewisi 



D. Spire elevated, sinistral. 



a. Rather wide in proportion to height, last whorl usually constituting larger part of 

 shell. Physa spp. 



