206 PROCEEDINGS OF THE ACADEMY OF 
H. hirsuta (pl. IX., fig. 6) has 22—1—22 teeth; 10 perfect 
laterals. . 
H. germana (pl. IX., fig. 5) has 28—1—28 teeth; 12 perfect 
laterals. Fig. 6 shows one of the few marginals which have the 
outer cusp bifid. 
H. monodon (pl. [X., fig. 4) has 21—1—21 teeth; 10 perfect 
laterals. Morse gives 28—-—-1—28 teeth. 
H. labrosa, maxillata, and Hdgariana not examined by me. 
Subgenus TRIODOPSIS. 
Jaw stout, arcuate, low, wide, ends but little attenuated, blunt; 
cutting margin without median projection; anterior surface with 
numerous decided, separated ribs, denticulating either 
margin. There are about 15 in palliata; 10 in ob- 
stricta; 15 in appressa; 14 in inflecta; 10 in Ru- 
geli; 14 in fallax ; over 10 in Hopetonensis ; over 12 
in Harfordiana; 11 in loricata ;' over 10 in triden- 
tata. I have not examined H. Mullani? and vultuosa. 
The subgenus is almost exclusively North American. ‘Two 
Central American species have, however, been described, and one 
European species, H. personata, Lam. ‘This last is said by Mo- 
quin-Tandon to have 3—-5 separated ribs upon its jaw, while our 
American species, as shown above, have numerous ribs. 
Triodopsis does not differ from Mesodon or Polygyra in the 
character of its jaw. Stenotrema, on the other hand, is readily 
distinguished by having the ribs broader and more crowded on 
its jaw. 
Appressa. 
Fig. 50. 
Lingual dentition of Helix appressa. 
The general arrangement of the teeth on the lingual membrane 
is shown in fig.50. The characters of the individual teeth are 
given on pl X. I have selected H. appressa (fig. 7) to show these 
1 The ribs are more crowded in this species. 
2 Probably identical with devia. 
