168 PROCEEDINGS OF THE ACADEMY OF 



Z. capsella (pi. III., fig. 4), 25 1 25 teeth, with 3 perfect 

 laterals, and one transition tooth. 



Z. fulvus. Morse gives 80 rows of 18 1 18 teeth, with 7 

 laterals. The specimen examined by me (from Orono, Maine) 

 h as 30 1 30 teeth with 8 perfect laterals. The difference in the 

 marginals is unusual for two individuals of the same species. 



The peculiarity of the lingual is the bifurcation of all the mar- 

 ginal teeth. On pi. XVII., fig. 5, I have drawn one central with 

 its adjacent lateral, and one marginal extracted from a Maine 

 specimen. 



By the bifurcation of the marginals this species is allied to Z. 

 Gu7idlachi,v?hich, however, has even some of its marginals tricus- 

 pid, and tricuspid laterals. 



The American form here under consideration was described by 

 Mr. Say under the name chersina. Judging from its shell alone, 

 it seems identical with the European L. fulvus. It has thus been 

 considered one of the circumpolar species common to the three 

 continents. My confidence of this identity is now shaken by a 

 study of the description and figure by Lehmann (Lebenden 

 Schnecken, etc., p. 79, pi. X., fig. 24), of the dentition of the Eu- 

 ropean Z. fulvus. He gives 86-100 rows of 25 1 25 teeth, the 

 first two laterals he makes tricuspid, while they are only bicuspid 

 in our form. The marginals appear to be bifid. The question of 

 identity must therefore be considered as still open. 



Z. Fabricii, not examined. 



Z. Gundlachi (pi. III., fig. 10, &, shows two marginals from two 

 adjoining transverse rows), 23 1 23 teeth, with 4 perfect laterals. 

 This lingual is peculiar in having its marginals bluntly bifid, as 

 in Nanina and Vitrina. Some of the marginals are even trifid. 

 The laterals are also tricuspid. 



Z. Stearnsi, not examined. 



Z. gularis (pi. III., fig. 1), has 30130 teeth, with 10 perfect 

 laterals. 



Z. siippressus (pi. XVI., fig. 2, b are marginals from near the 

 edge of the membrane). Teeth 30130, with 8 perfect laterals. 



Z. lasmodon (pi. III., fig. 7, b the smaller figure shows the 38th 

 tooth). Teeth 41141, with 9 perfect laterals. 



Z. signifcans (pi. XVII., fig. 10). 16 116, with 2 perfect 

 laterals. 



