THE NATURAL HISTORY SURVEY. 227 



surface with about thirteen heavy ribs, which denticulate both 

 margins (Fig. 60, J). 



Radula formula: ^+++4+^ (13-1- 13); the cen- 

 tral tooth has a rather wide base of attachment, attenuated at 

 the lower outer corners and excavated on the lower border; 

 the reflection is tricuspid, of which the center cusp is long and 

 narrow, reaching to the lower edge of the base of attachment; 

 the side cusps are very short. Lateral teeth similar to central 

 tooth, but bicuspid, the inner cusp long and the outer cusp 

 very short; the fifth lateral is modified by the shortening of 

 the outer cusp. The marginal teeth are low and wide and 

 denticulated by from three to five teeth, of which the inner is 

 the largest and bifid. The cutting points of the central and 

 lateral teeth are very short (Fig. 60). There are over 75 rows 

 of teeth. 



Genitalia : Unknown. 



Distribution: United States and Canada, from Maine to 

 Manitoba and south to Texas. 



Geological distribution: Pleistocene; Loess. Upper Eocene 

 of Isle of Wight. 



Habitat: Found on the edge of woodlands under and 

 about pieces of wood and various kinds of debris. 



Remarks: This is a most characteristic species, which 

 cannot be mistaken for any other. The peculiar parietal ribs 

 are different from any other species found in our region. The 

 animal is very slow and deliberate in movement and the shell 

 appears to be much too large for it. The latter is carried 

 perfectly flat and the animal moves about in a wabbly manner. 

 This species seems to be confined to the northern and western 

 regions. It has been seen by Mr. Jensen to prey upon Euconulus 

 fulvus. 



KEY TO SPECIES OF PUPID^.* 



A. Aperture without teeth or folds marginata 



B. Aperture with teeth or folds. 



a. Aperture squarish or rounded. 



1. Teeth few or wanting; never more than two, placed 



on the parietal wall corticaria 



2. Teeth numerous (five to seven), parietal tooth bifid 

 or bicuspidate; one or two basal teeth. 



fTeeth small, long, narrow, sharp, five in number, 



never filling the aperture; only one basal tooth procera 



ttTeeth large, massive, almost or quite filling 



the aperture. 



*Excepting Strobilops. 





