208 PROCEEDINGS OP THE ACADEMY OF 



quite blunt. Other portions of the membrane would furnish much 

 more sharply pointed teeth. 



H. appressa (pi. X., fig. 7) has 33 1 33 teeth ; about 12 perfect 

 laterals. 



H. inflecta (pi. X., fig. 4) has 22 1 22 teeth ; 7 perfect laterals. 

 This and the following species have inner marginal teeth with 

 simple, not bifid, cutting points (c). 



H. Rugeli (pi. X., fig. 3) has 21 1 21 teeth ; 6 perfect laterals. 



H. tridentata (pi. X., fig. 1) has 25 1 25 teeth ; 10 perfect 

 laterals. The inner cutting point is bifid after the 10th. 



H. Mullani. The species is probably identical with devia. 



H. Harfordiana has 26 1 26, with 12 laterals. Jaw with over 

 12 ribs. Received too late for illustration. 



H. fallax (pi. X., fig. 5) has about 40 1 40 teeth ; 14 laterals. 

 This (not tridentata) had no bifurcation to the inner cutting point 

 of the transition teeth, at least on the portion of the membrane 

 examined by me. 



H. introferens not examined by me. 



H. Hopetonensis (pi. X., fig. 6) has 27 1 27 teeth as far as I 

 can judge from an imperfect membrane. There are 7 perfect 

 laterals. 



H. vultuosa ,not examined. 



H. loricata (pi. XVIII., fig. 4) has over 20120 teeth ; 8 

 perfect laterals. 



Helix personata is the only European species of this subgenus, 

 but no figure of its dentition has been published to compare with 

 that of our species. The same is true of the two Central American 

 species known. 



Subgenus Mesodon. 



Jaw stout, high, arcuate, wide, ends but little attenuated, blunt ; 

 no median projection to the cutting margin ; anterior surface with 



numerous, separated, decided ribs, 

 Fig. 51. denticulating either margin. I have 



counted 13 in H. major ; 10 in albola- 

 bris ; 10 mmxdtilineata ; 11 in Pennsyl- 

 vanica; 12 in Mitchelliana ; 12 in 

 elevata; 13 in Clarki ; 13 in exoleta; 

 Jaw of Helix Sayu. [Morse ] 1 8 in Wetherbyi : 14 in dentifera ; 



