334 THE CHICAGO ACADEMY OF SCIENCES. 



gait. It is widely distributed throughout the area. At several 

 points in Chicago it has been found among Pleistocene fossils. 



1343. Amnicola limosa parva Lea, pi. xxxi, fig. 11. 



Amnicola par-va LEA, Proc. Amer. Phil. Soc., Vol. II, p. 34, 1841; 

 TRYON, Con. Haldeman's Monograph, pi. xvii, fig. 2. 



Shell: Smaller than typical limosa, the whorls shouldered 

 and tumid below the suture. Otherwise like limosa. 



Length, 3.50; width, 2.75; aperture length, 2.00; width, 1.50 mill. (10218.) 

 3.25; " 2.00; " " 1.50; " 1.25 (10218.) 



Animal and Dentition: Same as limosa. 



Distribution: Atlantic and Middle States. 



Geological distribution: Pleistocene. 



Habitat: Same as limosa. 



Remarks: This form is found at Joliet, Salt Creek and 

 Berry Lake; the writer has admitted it to varietal rank for the 

 reason that it seems to be always recognizable, although it is 

 apparently only a stunted form of limosa. It is not common. 



i34b. Amnicola limosa porata Say, pi. xxvi, fig. 13. 



Paludina porata SAY, Journ. Phil. Acad., Vol. II, p. 174, 1821. 

 Amnicola orbiculata LEA, Proc. Amer. Phil. Soc., Vol. II, p. 34, 1841. 



Shell differing from limosa in being generally widely um- 

 bilicated, in the whorls being more swollen and the spire 

 shorter. 



Length, 5.00; width, 4.00; aperture length, 2.80; width, 2.10 (13357.) 

 5.00; " 4.50; " " 2.80; " 2.05 (13357.) 



This variety is the most common and is universally dis- 

 tributed. 



135. Amnicola lustrica Pilsbry, pi. xxvi, fig. 12. 



Amnicola lustrica PILSBRY, The Nautilus, Vol. IV, p. 53, 1890 (not A. 

 lustrica SAY Pomatiopsis lapidaria SAY). 



Shell: Narrow (for the genus), thin, translucent; color 

 waxy, light brownish or greenish; surface smooth and shining, 

 lines of growth very fine, but distinct when viewed with a lens; 

 sutures very deeply impressed; spire elevated, conical; whorls 

 five, rounded, regularly increasing in size; aperture roundly 

 ovate, slightly angled above, waxy inside; peristome continu- 

 ous, thin, appressed to the body whorl only for a short distance 

 near the upper terminations; base broadly rounded, with a 

 narrow and deep umbilicus. Operculum similar to that of 

 A. limosa. 



