NATURAL SCIENCES OF PHILADELPHIA. 221 



angle of the base of attachment ; outer laterals with a more 

 developed cutting point and a decided side cusp and cutting point; 

 the change from the laterals to the marginals is shown in the 16th 

 tooth (see fig. 63), where the base of attachment is wider, the 

 reflection stouter and the inner cutting point becomes bifid. The 

 marginals are low, wide, the reflection equalling the base of 

 attachment, the inner cutting point short, bluntly bifid, the outer 

 shorter and blunt. 



Lingual dentition of Helix hortensis. [Morse.] 



Having no specimen to examine myself, I am dependent on 

 Morse's figures given above. 



Subgenus Pomatia. 



Jaw of our only species, H. aspersa, introduced by commerce 

 at Charleston, S. C. (where it is still common), high, thick, arcuate, 

 ends but little attenuated, blunt; cutting margin without median 

 projection ; anterior sui-face with 6 stout, separated ribs, deeply 

 denticulating either margin (pi. XVI., fig. 8). 



Lingual membrane of the same species (pi. XIII., fig. 7, a, 6, c) 

 long and narrow. Teeth 50 I 50, with 15 perfect laterals. 

 Centrals with base of attachment longer than wide, the lower 

 lateral angles but slightly produced, the lower margin in some 

 cases with a quadrate excavation or thinning as usually found in 

 Succinea ; the upper margin broadly reflected, reflection very 

 large, with a very stout, short median cusp, bearing a short, stout 

 cutting point reaching the lower edge of the base of attachment ; 

 side cusps obsolete, but bearing well developed, short side cutting 

 points. Laterals like centrals, but unsymraetrical by the sup- 

 pression of the inner, lower, lateral angle of the base of attach- 

 ment, and the inner side cutting point. Transition teeth from 

 the laterals to the marginals (6) with a more developed reflection, 

 a shorter inner cusp bearing a greatly developed bifid cutting 

 point. Marginals (c) low, wide, the reflection equalling the base 



