274 THE CHICAGO ACADEMY OF SCIENCES. 
length of the entire shell; sutures well impressed; aperture 
roundly-ovate, more or less expanded; peristome thin, acute, 
sometimes expanded, in old specimens thickened by a heavy 
deposit within; the peristome is white and there is a band of 
very dark brown which edges the callus deposit; columella 
oblique, reflected, with a large fold across the middle, and cov- 
ered by a heavy, whitish, testaceous deposit which is more or 
less spreading; umbilicus closed by the spreading callus and 
reflected columella, but the region is indented and the umbili- 
cus is sometimes narrowly open, 
Length, 27.50; width, 9.50; aperture length, 12.00; width, 5.00 mill. (9323.) 
“93.00; 9,00; 11.00; “ 5,00 “ (8114.) 
“ 9400; “ 10,00; “11.50; “ 5.50 “  (9884,) 
«30.00; “ 12.00; «“ “1400; “ 710 “ (8115,) 
«96.00; “ 12.00; “1995: 7.00 “ 8115.) 
“90.00; “ 900; « “9.00; = 4.50“ (9695.) 
ORE Le, | apie Eo, RI Stee “850; “© 8.50 “ (9695.) 
“ 96.50; “ 11.00; “11.00; “ 6.00 “ (9695.) 
Animal: With ashort, wide foot, rounded before and be- 
hind; tentacles short, triangular; color black, lighter below, 
the body spotted with white which shows through the shell. 
Heart situated as usual, pulsations regular, eighty to eighty- 
one per minute. Length of foot 8.00, width 3.00 mill. 
Jaw: As usual. 
Radula formula: ¥4+$+$+4+$44+4 (34—1—34); cen- 
tral tooth as usual; lateral teeth of the usual type, bicuspid; 
transition teeth at first like laterals but tricuspid, the central 
cusp the largest (eleven) but soon (thirteen) the inner cusps 
become more equal and the outer cusp small; marginal teeth 
of the usual type (Fig. 89). In one membrane examined 
(Fig. 90) the first lateral to the right of the central tooth hada 
bifid outer cusp. This was observed in all the first laterals in 
this membrane. 
Genitalia: Not observed. 
Distribution: North America, Europe, Asia; circumpolar. 
Alaska (Randolph). 
Geological distribution: Pleistocene; Loess. 
Habitat: Found in small streams and rivers, ponds and 
lakes, attached to floating sticks and submerged water plants. 
Remarks: This is a very common and also a very variable 
species. It is always a wide, more or less fusiform species, 
with the aperture and spire equal, or the latter a trifle longer, 
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