EASTERN PROVINCE — INTERIOR REGION SPECIES. 249 



within certain limits in different individuals of the same species. I 

 have repeatedly found this to be the case. 



In regard to the generic value of the type of lingual dentition, I can 

 only say in general terms that within certain limits it may prove relia- 

 ble. Here, again, however, we find the type of dentition inconstant 

 when many species are known. Thus, in Arionta we find Townsendiana 

 quite differing from the other known species (see p. 126). In Mesodon, 

 also, I find two quite distinct types of dentition, and under each genus 

 I have i^ointed out the variation observed. I am convinced that the 

 presence or absence of side cusps to central and lateral teeth is not a 

 reliable generic character. The same may be said of the side cutting 

 points. The marginal teeth offer more reliable characters. They are 

 very peculiar in VaUonia and Strohila, in being very low and wide and 

 having numerous cutting points, quite resembling those of Pupa. In 

 MesodoUj Triodopsis, and Arionta the marginals are longer than wide, 

 with only two, sometimes bifid, cutting points. In Stenotrenui and Fo- 

 lygyra they are rather wider than long, also with two more bluntly bifid 

 cutting points. It must be borne in mind, however, that my observations 

 have not led me to believe these characters sufficiently constant to be 

 of generic value. There is also some variation in the mode of passing 

 from lateral to marginal teeth, even in the same genus, in some cases 

 the transition being made simply by a gradual modification of form, in 

 others by the splitting of the inner cutting point. These points will 

 be treated more fully under each genus. 



DOUBTFUL, SPURIOUS, EXTRALIMITAL SPECIES OF HELIX. 



The following list does not contain the names of our si3ecies of dis- 

 membered Helix : 



Helix (Sheppard, Trans. Lit. and Hist. Soc. Quebec, i, 194). Shell thin, co- 



noiclal, perforated ; spire very flat ; margin of lip reflected. 



Common in the same place as the above {H. horfensis, Plains of Abraham, 

 Quebec); it is a much less shell, with a brown epidermis; the i>enultimate 

 whorl has an elevated white ridge near the aperture, which appears to be 

 some remains of the last year's lip. (Sheppard.) [= ST. ru/escras ?") 



Helix Sagraiava, D'Orbigny, a Cuban species, is erroneously attributed to California 

 (on the authority of Sowekby) by Pfeiffer (Mon., i, 325) and Carpenter 

 (Report, 214). 



Helix Sandiegoensis, Lea, is mentioned by name only by Gould, Pac. R. E. Eep., v, 

 331. 



Helix attenuata, Lake Superior, &c., is given, without description, by J. de C. Sow- 

 erby, iu Richardson's Fauna Boreali- American a (iii, 315), together with 



Helix gularis, 



Helix rudis, and 



Helix paludosiit (= H. minuta). 



