268 THE CHICAGO ACADEMY OF SCIENCES. 



and elongately-ovate aperture. It approaches Z. humilis in some 

 of its forms, but that species is much smaller, has a shorter, 

 more obtuse spire, and a more rounded base and aperture; the 

 lower part of the latter is not produced as in desidiosa. When 

 in motion the animal is slow and deliberate, the shell being 

 pulled forward by a series of jerks. It is a very common Lim- 

 ncea, and is found in all parts of the area. Fossil forms occur 

 in sand banks on'the lake shore north of Graceland avenue. 



The spire and shell vary greatly in length and width, in 

 some cases being long and narrow while in others they are 

 shorter and the whorls more rounded. So great is this varia- 

 tion that, did not intermediate forms occur, the extremes would 

 be worthy of specific distinction. The rounder, more graceful 

 forms are figured on PI. xxxi, Fig. 7. 



108. Limnaea humilis Say,* pi. xxx, fig. 21. 



Limncsa humilis Say, Journ. Phil. Acad., Vol. II, p. 378, 1822. 



Limncea parva LEA, Proc. Amer. Phil. Soc., Vol. II, p. 33, 1841. 



Limncea curta LEA, 1. c., p. 33, 1841. 



Limncea exigua LEA, 1. c., p. 33. 1841. 



Limncea griffithi an a, LEA, I.e., p. 33, 1841. 



Limncea linsleyi DE KAY, Moll, of New York, p. 72, pi. iv, fig. 74, 1843. 



Limncea lecontiiLv.\ t Proc. Phil. Acad., p. 113, 1864. 



Shell: Thin, transparent to translucent, ovate-conic; color 

 light horn, sometimes reddish; surface shining, covered with 

 numerous crowded lines of growth, which are not much ele- 

 vated and which disappear on the apex; whorls five, well- 

 rounded, the last being a trifle longer than the spire in most 

 specimens; spire obtusely conic; sutures impressed, sometimes 

 indented; aperture oblong-ovate, somewhat expanded, nar- 

 rowed at the upper part, generally a little longer than the 

 spire; peristome thin, acute; columella oblique, covered with 

 a thin testaceous deposit; the columella is reflected along the 

 lower third, the reflection nearly covering the umbilicus which 

 is narrowly open. 



Length, 8.50; width, 4.00; aperture long, 4.50; width, 2.75 mill. (10488.) 

 8.00; " 450; " " 4.50; " 2.25 " (10488.) 



7.25; " 3.50; " " 3.75; " 2.00 " (10488.) 



Animal: In general form similar to desidiosa; color light 

 brown or blackish, lighter on the foot, translucent about the 

 edges of the body. Heart situated as in the last species, pul- 



*It is probable that some names here given as synonyms will be found to constitute 

 good varieties when a revision of the genus is made from abundant and authentic material. 

 The same, is true of L. desidiosa. 



