236 THE CHICAGO ACADEMY OF SCIENCES. 



all of the cusps have well developed cutting-points (Fig. 66).* 



Genitalia: Not examined. 



Distribution: Entire Northern United States, Ontario, 

 Canada, and Eastern Mexico. 



Geological distribution : Pleistocene. 



Habitat: Found plentifully under chips and stones, in rot- 

 ting logs, etc., on the edge of forests. 



Remarks: Distinguished from B. armifera by its smaller 

 size, triangular aperture, and especially the massive parietal 

 tooth which nearly fills up the aperture. The keeled base is 

 also a distinguishing feature. From B. holzingeti it is separated 

 by its carinated base, fewer teeth in the aperture and their dif- 

 ferent form. It is a very abundant species and of much inter- 

 est when studied alive. The shell is carried well upright and 

 the motions of the animal are generally slow and methodical. 

 Frequently when crawling over a table it will lift up its head 

 and a portion of its body until only the tail rests on the sur- 

 face. It is very widely distributed, being found in all the 

 regions. 



93. Bifidaria holzingeri Sterki. Text, fig. 67. 



Pupa holzingeri STERKI, The Nautilus, Vol. Ill, p. 37, 1889. 

 Pupa holzingeri fordiana STERKI, The Nautilus, Vol. VI, p. 4, 1892.J 

 (Variety). 



Shell: Small, cylindrical, turreted, shining, minutely um- 

 bilicated; growth lines (striae) minute, oblique; nucleus smooth; 

 color whitish, vitreous; whorls five, convex, regularly increas- 

 ing, the last two of about equal size and the first three forming 

 a rather pointed apex; the last whorl is narrowed and descends 

 slightly toward the aperture, and the base is considerably com- 

 pressed but not keeled as in contracts; just back of the aper- 

 ture there is an oblique, elevated ridge formed by a white 

 callus, which follows the direction of the growth lines, and ex- 

 tends from the suture to the base; behind this ridge the body 

 whorl is flattened and impressed by one of the teeth; sutures 

 well impressed; aperture lateral, "inverted subovate, with a 

 slight sinus at the upper part of the outer wall;" six-dentate as 

 follows: one on the parietal wall, large, long, high, curved out- 

 ward about the center, bifurcated, "the outer branch reaching 

 the parietal wall;" one on the columella, high, longitudinal, 



*The descriptions of some of the radulce here enumerated were first given in Journ. Cin. 

 Soc., N. H., Vol. XIX. No. 3. pp. 81-89. 1897. 



tThis'is the only reference the writer is able to find concerning this variety. 



