THE MOLLUSCA OF COLORADO 93 



(Owing to unsatisfactory status of species of this genus it is deemed best not to attempt 

 to differentiate them in this key.) 



b. Distinguished from Physa by long, narrow form, very highly polished shell and sim- 

 ple mantle margin of animal, spire long, body whorl subcylindrical, height of shell 

 lo to i8 mm., width s to 9 mm. Apleia hypnorum 



E. Spire elevated, dextral. 



a. Adults under 20 mm. in height, coliunella without well-marked fold. 

 aa. Columellar lip not broadly reflected. 



1. Rather slender, growth lines numerous with usually some coarser wrinkles, 

 sometimes faceted by a few coarse spiral wrinkles intersecting growth 

 lines, aperture narrow and half the length of shell or more, base rather 

 produced, whorls 5, height 8 to 13 mm. Lymnaea obrussa 



2. Short spired form of obrussa Lymnaea obrussa modicella 



3. Smaller, spire shorter and less sharp, base less produced than in obrussa, 

 whorls 5, height 7 to 9 mm. Lymnaea humilis 



4. Growth lines fine and numerous, latticed (under lens) by fine, raised inter- 

 secting spiral lines, whorls 5 or 6, more convex than in obrussa, aperture 

 shorter and more nearly circular, height 10 to 15 mm. Lymnaea caperata 



bb. Columellar lip broadly reflected. 



1 . More slender than humilis, spire longer and more turreted, aperture more 

 regularly elliptical. Lymnaea parvus 



2. Smooth, shorter than obrussa in proportion to height, aperture somewhat 

 longer than caperata, growth lines not crossed by spiral raised lines, whorls 

 5, height 9 mm., width 5 mm. Ljrmnaea bulimoides 



3. Spire shorter, form more globose, umbilicus larger than bulimoides. 



Lymnaea bulimoides cockerelli 



4. Spire acutely conic, whorls 5 or 6, finely striate, usually malleated, facets 

 obliquely descending, umbilicus large, columellar lip very broadly reflected. 



Lymnaea bulimoides techella 



b. Adults over 20 mm. in height, with distinct oblique fold across columella. 



aa. Very large, whorls 6^, last large and inflated, spreading columellar callus 



closely appressed, completely covering umbilicus. 



Lymnaea stagnalis appressa 



bb. Smaller, whorls 6, last not so large in proportion to spire, columellar callus not 

 entirely covering umbilicus. 



1. Growth hnes crowded, crossed by numerous fine, incised spiral lines and 

 sometimes several coarse, elevated wrinkles, whorls rather flat, peristome 

 thin, white, with brown band edging callus within. Lymnaea palustris 



2. Very long spire, whorls flat. Lymnaea palustris elodes 



3. Body whorl and aperture wider, whorls rounded and somewhat shouldered. 



Lymnaea sumassi 



