2 Trans. Acad. Sci. of St. Louis. 



C. Shell 10 to 20 mill, in length. 



a. Surface marked with distinct, impressed spiral lines. 



1. Spire longer than aperture, shell attenuated. caperata. 



2. Spire equal to aperture, shell globose in form. cubensis. 



3. Spire half the length of the aperture. columella. 



b. Surface without distinct spiral lines. 



1. Spire equal to or longer than aperture. 



t Spire short conic, aperture roundly ovate, not produced, humilis. 

 ft Spire long and pointed, aperture long-ovate, produced, desidiosa. 



2. Spire shorter than aperture. 



t Spire bluntly rounded, shell very globose. catascopium.* 



A recent study of numerous species of this genus has con- 

 vinced the writer that some classification other than the one 

 in use must be found. The present grouping by shell char- 

 acters is totally unsatisfactory on account of the extreme 

 variability of the individuals. For example, different forms 

 of L. emarginata Say var. mighelsi Binney, recently exam- 

 ined, can be placed in all of the so-called subgenera usually rec- 

 ognized (Radix, Bulimnea, Limnophysa, etc.) and in fact 

 the typical emarginata is typical of Limnophysa, and the 

 variety mighelsi of Radix; all of the intermediate forms occur 

 and absolutely connect the extremes. In view of this fact the 

 writer has discarded all subgenera, using simply the generic 

 term Limnaea. Some divisions of value undoubtedly will be 

 found when all of the species are examined anatomically, for 

 the genitalia, radula, etc. There is abundant work in this line 

 for a naturalist having the time and material at his command. 



1. Limnaea columella Say. 



Pi. I. f. J 3. 



Limnaea columella Say, Journ. Phil. Acad. 1 : 14. 1817. 



Limnaea navicula Valenciennes, Rec. d'Obs. 2 : 251. 1833. 



Limnaea chalybea Gould, Am. Journ. Sci. i. 38 : 196. 1840. (Variety.) 



Limnaea acuminata Adams, 1. c. 39 : 374. 1840. 



Limnaea strigosa Lea, Proc. Amer. Phil. Soc. 2 : 33. 1841. 



Limnaea coarctata Lea, 1. c. p. 33. 1841. 



Limnaea casta Lea, 1. c. p. 33. 1841. (Variety.) 



Succinea pellucida, Lea, Proc. Phil. Acad. 1864 : 1C9. 



Limnaea columellaris Adams, Amer. Journ. Sci. i. 36 : 392, absq. descr. 



Limnaea succiniformis Adams, ms. teste Haldeman. 



Shell: Ovate, somewhat pointed, thin, fragile, transparent ; 

 color light greenish or yellowish horn ; surface shining, cov- 



* The long spiral form is not found in this region. 



