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 a sixth, 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.) 

 " 1.50; " 0.90; " " 0.40 " (11993.) 



Animal: As v& pentodon. 



Jaw: Not differing from that of pentodon. 



Radula: 10 I 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. 



