290 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



Helix polygyrella, Bland & Cooper, Ann. N. Y. Lye., VII. 365, PI. IV. Figs. 



13-15 (1861). — W. G. Binney, L. k Fr.-W. Sh., I. 112 (1869). 

 Polygyra polygyrella, Tryon", Am. Journ. Conch., III. 160 (1867). 



Central Province. Common on the Coeur d'Alene Mountains, especially on 

 their eastern slope, in spruce forests. 



Jaw and lingual membrane (see p. 289). 

 Genitalia unknown. 



STENOTREMA, Raf. 



Animal heliciform, mantle subcentral ; other characters as in Patula. 

 Shell with the perforation covered, lenticular or globosely depressed, hairy ; 

 whorls 4^-6, the last anteriorly gibbous, shortly deflexed, tumid below; spire 

 somewhat elevated ; peristome with a white, thickened margin, briefly reflexed 

 above, somewhat constricted in its basal portion, usually sinuous and dentate, 

 furnished with an internal transverse tubercle on the floor of the base of the 

 last whorl. 



A North American genus, meeting its greatest development in the Cumber- 

 land Subregion. 



Jaw thick, high, arched; ends but little acuminated, blunt ; cutting margin 



without median projection ; anterior surface with stout, broad, crowded ribs, 



denticulating either margin. There are about 8 in 



Fig. 188. stenntremnm, 11 in germanum, 1 7 in monodon, 8 in hir- 



sutum, 13 in Edvardsi, 12 in barbigerum, 8 in .spino- 



sum, 12 in labrosum. 



^^ I have had no opportunity of examining Edgarianarn 



Jaw of S. monodon 



(Morse). °r maxiuatum. 



The subgenus is restricted to North America as far 

 as known. It differs from our other subgenera in having its ribs much 

 broader and much more closely crowded. 



Lingual membrane arranged as in Patula. Centrals with a base of attach- 

 ment longer than wide, the lower lateral angles but little expanded, the lower 

 margin incurved, the upper margin squarely reflected ; reflection large, wide, 

 with small, in some species almost obsolete, side cusps, always bearing distinct, 

 well-developed cutting points ; and a very stout median cusp, bearing a stout 

 cutting point which usually projects beyond the lower edge of the base of 

 attachment. Laterals like the centrals, but asymmetrical by the suppression 

 of the inner lateral angle of the lower edge of the base of attachment and the 

 inner side cusp and cutting point. The transition from laterals to marginals is 

 shown in PI. VII. Fig. B (S. spinosum). It is, as usual, produced by the com- 

 parative lesser development of the inner cusp and greater development of its 

 cutting point. This cutting point becomes bifid, the reflection becomes 



^ ! See Ann. Lye. N. H. N. Y., X. PI. XIV. Fig. 4. Perhaps a Mesodon. 



