268 THE CHICAGO ACADEMY OF SCIENCES. 
andelongately-ovateaperture. ItapproachesZ. hwmilisin 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 aseries of jerks. Itisa very common Limn- 
nea, 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. Limnza humilis Say,* pl. xxx, fig. 21. 
Limnea humilis Say, Journ. Phil. Acad., Vol. II, p. 378, 1822. 
Limnea parva LEA, Proc. Amer. Phil. Soc., Vol. II, p. 33, 1841. 
Limnea curta LEA, |. ¢c., p. 33, 1841. 
Limneaexigua LEA, |. c., p. 33. 1841. 
Limnea grifiithiana, LEA, |.c., p. 33, 1841. 
Limnea linsleyi DE KAY, Moll. of New York, p.72, pl. iv, fig. 74, 1843. 
Limnea lecontii LEA, 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: Re «ADD. 8 BR Ae 
Be y fs eee Fa, cf 6) eee See 2.00 “ (10488.) - 
Animal: In general form similar to destdiosa,; 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 
goad varieties when a revision of the genus is made from abundant and authentic material, 
he same is true of L. desidiosa., 
