NATURAL SCIENCES OF PHILADELPHIA. 



201 



Lingual membrane with 14 114 teeth, 5 laterals. All the 

 teeth like those of if. labyrinthica (pi. XVIII., fig. 11). 



There are no known species foreign to North America, with 

 which to compare the dentition and jaw of labyrinthica and 

 Hubbardi. 



Fie. 45. 



Jaw of Helix 

 ventrosula. 



Subgenus Polygyra. 



Jaw high, arcuate, ends scarcely attenuated, blunt, cutting edge 

 without median projection ; anterior surface with numerous stout, 

 separated ribs, denticulating either margin. I have 

 counted 8 ribs in H. ventrosula; 14 in pastula; over 

 14 in cereolus ; 10 in espiloca ; 13 in uvulifera ; 10 

 in Texasiana; 12 in Troostiana ; 11 mleporina; 15 

 in Mooreana; 20 in fastigans ; 7 in septemvolva ; 10 

 in FeMgeri; in Hazardi, auriculata, and auriformis 

 they are also numerous. I have had no opportunity of examining 

 the jaw in the other species found within our limits, Poslelliana, 

 avara, Hindsi, triodontoides, tholus, hippocrepis, oppilata, Dor- 

 feuilliana, Ariadnee, cereolus (see p. 203), Garpenteriana (see ib.), 

 pustuloides. 



By the character of its jaw, Polygyra can be compared only to 

 Triodopsis and Mesodon among the other North American sub- 

 genera of Helix. No foreign species has yet been examined. The 

 genus is almost exclusively North American, though several species 

 have been described from the West Indies and Mexico, and one 

 from Bolivia. 



Fi^. 46 shows the general arrangement of the teeth upon the 



Fig. 40. 



Lingual dentition of Helix auriformis? [Leidy.] 



lingual membrane, the characters of the individual teeth being 

 better shown in my plate VIII. The teeth do not differ from what 

 I have described under Stenotrema (see p. 205). As in all the sub- 

 genera, there is considerable difference in the length of the base 

 of attachment on the eentral and lateral teeth in the several 

 species. 



The marginals are lower and wider (see pi. VIII.,.fig. 1, d) than 

 14 



