174 AMERICAN JOURNAL 



intending to leave the choice of the others an open question, 

 and to use "Helix" (nearly in the Linnaean sense), for the 

 banded groups. I have since, however, adopted all the generic 

 names of the Helicellinae groups (in the " Geographical Cata- 

 logue of the Mollusca," &c), because I believe most of them 

 have been confirmed by Morse's dissections, and comparison of 

 the animals with those of the genera founded on European 

 types, Hyalina. Gonulus and Patula. These, too, are almost 

 continually connected on the two continents by circumpolar 

 species scarcely distinguishable. There is some doubt, how- 

 ever, whether Newherryana, chersinella, Hornii, polygyrella or 

 Idalioensis really belong to the genera I have assigned them to. 

 As to the banded species, I have retained " Helix' until I can 

 compare the animals with European types, although the type of 

 that genus is also European, and perhaps distinct from any 

 American generic form. Here comes the question, " what is 

 the type of Helix?" I cannot find here an early edition of 

 Linne's " Systema," but some of his first copyists placed lapi- 

 cida at the head of the genus. The French authors generally 

 used Helix as we use Helicidce and divided the species into 

 genera with other names, so that lapicida became a Carocolla, 

 and the pomatia group was considered typical, an arrangement 

 followed by most modern authors. I think, however, that Beck 

 restored lapicida to Helix, and made the genus Pomatia to in- 

 clude the latter group, an arrangement which must be adopted 

 if they are decided to belong to distinct genera, and if Lin- 

 naeus placed lapicida at the head of his genus Helix when 

 founded, otherwise, there is nothing to prevent any author from 

 choosing any species as the type of the genus.* 



As to Mesodon, I think Rafinesque did not intend to include 

 in.it the species with a tooth on the "columella" or body whorl, 

 but this " lower lip with a tooth," referred to the tooth seen in 

 profunda, which would be his type, while Odotropis would in- 

 clude many usually called Mesodon, having the characters of 



* Note. — Upon examining the 12th Edition of Linnaeus, I find the first 

 species there under Helix to belong to the genus Scarabus ! The second 

 species is lapicida, pomatia the twenty-second. It is well known that La- 

 marck's first species of Planorbis is Ampullaria cornu-arietes. Several 

 American naturalists of distinction refuse to recognize the rule to take the 

 first species of a genus as the type in all cases, alleging, with very good 

 reason, that in many cases (as above) it would make great confusion in 

 the synonymy. They prefer to recognize the " law of exclusion :" i.e. 

 taking from the genus all the species that have been placed in other 

 well-recognized genera, they adopt as the type the first remaining 

 species. — Editor. 



