HELIX. 



15 



Surface of 

 Belix alternata. 



Fig. 125. 124). I have also given a figure 

 (Fig. 125) of the magnified surface 

 of a strongly ril)bed form from 

 North Carolina, and a view (Fig. 

 126) of a strongly ribbed form 

 from the postpleioccne. 

 The jaw of H. alternata does not have the an- 

 terior ribs and crenulated concave margin characteristic of the 



genus. It is arcuate, equally broad 



in its whole length, with square ends ; 



anterior surface strongly striate both 



transversely and vertically ; concave 



margin not strongly crenulated, but 



having ho median projection. Both 



the jaws figured were taken from individuals of this species. 

 Lingual membrane with 121 waving rows of 34 — 1 — 34 teeth 



each ; centrals with one long, stout cusp, surmounted by an acute. 



Fi?. 127. 



Helix alternata. 



F\3. 128. 



Jaw oi HelLc alternata. 



Fig. 129. 



Lingual dciitition of Uelix alternata. [Mokse.] 



cone-like point, and two lateral, obsolete ones ; laterals of same 

 shape, but distinctly bicuspid ; uncini at first like the laterals, 

 but modified as they pass off laterally by the cusps becoming of 

 more equal length. 



