204 PROCEEDINGS OF THE ACADEMY OF 
reflected: reflection large, wide, with distinct, but small, rounded 
side cusps bearing short conical cutting points, and a very stout 
median cusp reaching the lower margin of the base of attachment, ! 
beyond which projects the short, stout, conical cutting point. 
Laterals like the centrals, but unsymmetrical by the suppres- © 
sion of the inner, lower angle of the base of attachment, and the 
inner side cusp and cutting point. First marginals a simple 
modification of the laterals by the lesser development of the cut- 
ting point (6). Outer marginals (c) low, wide, the reftection 
equalling the base of attachment and bearing one inner, short, 
stout, oblique cutting point, and two shorter outer blunt cutting 
points. 
Polygyrella is quite distinct from all the other American sub- 
genera of Helix by the form of its jaw and the large number of 
ribs upon its anterior surface. 
Subgenus STENOTREMA. 
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 stenotrema, 11 in 
germana,' 7 in monodon, 8 in hirsuta, 13 in 
Hdvardsi, 12 in barbigera, 8 in spinosa. 
7 “A I have had no opportunity of examining H. 
Jaw of Helix monodon. : ‘ 
[Morse ] labrosa, Edgariana, or maxillata. 
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. 
Fig. 48. 
Lingual dentition of Helix monodon. [Morse.] 
Fig. 48, drawn by Mr. Morse, gives the general arrangement of 
the teeth on the lingual membrane. The characters of the indi- 
vidual teeth are more correctly shown in my figures on pl. IX. 
1 See Ann. Lye. N. H. N. Y., X. pl. XIV., fig. 4. Perhaps a Mesodon. 
