240 THE CHICAGO ACADEMY OF SCIENCES. 
placed squarely on the base of the aperture; a fifth, larger, 
conical tubercle placed at the right-hand turn of the peristome 
and almost reaching the parietal tooth; and asixth, small, con- 
ical tubercle placed at about the middle of the outer lip; the 
callus connecting the terminations of the peristome is narrower 
and more curved than in pentodon,; other characters the same 
as in the other species (Fig. 69). 
Length, 1.50; diameter, 0.90; aperture length, 0.50 mill. (10645.) 
cor) SO: ty O.F0e) oi 4 0.40-. “* , (11998.) 
Animal: As in pentodon. 
Jaw: Not differing from that of pentodon. 
Radula: \o—1—10, in all respects like that of pentodon. 
Genitalia: Unknown. 
Distribution: Massachusetts to Minnesota; Ontario and 
Quebec, Canada, to Florida. 
Fig. 69. 
BIFIDARIA CURVIDENS Gould. (Binney, Fig. 347.) 
Geological distribution: Pleistocene; Loess. 
Habitat: In elevated localities, where moisture is reduced 
to a minimum. 
Remarks: This species is distinguished from B. pentodon 
by its smaller size and peculiar apertural armature, the teeth 
being fewer in number, and the parietal tooth larger and curved 
inwards. It is always smaller, the whorls less rapidly increas- 
ing, and generally has a decided crest on the parietal wall. It 
is not as common as the last species, but is more widely dis- 
tributed, being found in the three regions. 
Genus VERTIGO Draparnaud. 
“Animal as in Pupa, but tentacles wanting.” 
‘Shell deeply rimate, ovate,apex acuminate, obtuse; whorls 
5-6, the last rounded; aperture semioval, with 4 to 7 folds; 
peristome scarcely expanded, white-lipped;”* Jaw arched, 
ends squarely truncated, anterior surface striate, cutting edge 
with median projection. Radula with a central tooth almost. 
square, tricuspid, as large as or larger than the laterals, which 
*Binney, Man. Amer. L, S., p. 333. 
