THE NAUTILUS. 



21 



the foot by a short neck ; mouth large, in the lower plane of the 



head, showing plainly the jaw and 

 radula while the animal is grazing 

 alongthe side of an aquarium ; eyes 

 placed on swellings at the inner 

 base of the tentacles ; respiratory 

 cavity on left side of the shell at 

 the lower point where the peristome 

 meets the body whorl. Length of 



foot 15.00; width 4 mill, extended (Fig. 4). 



Jaw in one piece, arched, striated, provided with a central fibrous 



projection from the superior surface ; ends rounded (Fig. 5, J). 



FIR. 4. 



Eadula : Formula 



FIG. 5. 



9o Ju 1 95 95 ,, ,-,,-, , , 



- -I (190-1-190) ; central 



13^ 1 ^2-5-2^ 1 r J3 



tooth more or less quadrate, the lower outer corners being very much 

 attenuated ; cusp 9-dentate, 5 denticles being long and narrow, and 

 two on each side smaller and more blunt ; laterals in two alternate ser- 

 ies, the primary teeth large, obliquely inclined, comb-like ; the cusps are 

 very peculiar, and vary to a large degree ; some teeth have five long, 

 pointed cusps with six small ones, one between each large one and 

 one at each end (Fig. 5) ; others have but two small denticles, while 

 still others have one or more between (Figs. 5, 2, 3, 4). The 

 secondary teeth are long and narrow, with a wide, blunt cusp. 

 These latter, as also the central tooth and small teeth between the 

 cusps of the primary teeth, are very difficult to observe (Fig. 5). 



Distribution : Probably inhabits the whole of the northern and 

 central parts of the United States and Southern Canada. Geologi- 

 cal distribution : Pleistocene; Loess. Habitat: Found veryabund- 



