OF CONCHOLOGY. 81 



Mesomphix, 1819 (p. 27,*) — Embracing such species as H. 

 fuliginosa, inornata, demissa, ko,.^ together with many European 

 species. Characterized by a diaphanous texture, unreflected 

 lip, and large umbilical opening. 



Stenotrema, 1819 (p. 28.) — With a thick lip, emarginate, and 

 a second lip or callus on the body whorl, uniting with the 

 outer lip. — Ex. H. Imsuta, Say, and allied forms. 



Triodopsis, 1819 (p. 28.) — proposed for the tridentate species 

 of which H. tridentata, Say, may be considered the type. 



Mesodon, 1831 (p. 67.)— "Differ from Helix by lower lip 

 with a tooth," referring to the species of the alholahris group, 

 all of which exhibit this character in greater or less distinctness. 



The following genera have not been adopted : — ■ 



O-lotropis, 1819 (p. 27.) — Shell with a tooth on the colu- 

 mella, lip reflected and covering the umbilicus. This genus 

 was instituted for such shells as S^. alholahris, H. exoleta, etc., 

 but tlie characters are not in all cases of even specific value, 

 and the species have very properly been included in Mesodon. 



Xolotrema, 1819 (p. 27.) — Differs from Triodopsis by having 

 a covered umbilicus, and the inferior tooth lamelliform. This 

 genus, intended to embrace H. palliata, H. ohstricta, H. ap- 

 jyressa, &c., has been considered synonymous with Triodopsis. 

 We think, however, that the group of shells included by its 

 characters are sufficiently distinct to retain the name imposed 

 by Rafinesque, and have so separated them in our Cabinet. 



Ghimotrema^ 1819 (p. 28.) — With a transverse covered aper- 

 ture, resembling a simple fissure. 



Toxotrema^ 1819 (p. 28.) — Differs from the preceding genus 

 by an emarginate lip. Both these genera are referable to 

 Stenotrevia, Raf. 



Aplodon, 1819 (p. 28.) — Umuilicated, aperture rounded, col- 

 umella toothed. This genus is a synonym of Mesodon^ and 

 would include such species as H. thyroides. 



Omphalina, 1831 (p. 67.) — " Differ from Helix by no lips, 

 but an orabilic." Appears to be the same as Mesomphix. 



Tropliodon and Odomphium^ 1831 (p. 67,) are both forms of 

 Mesodo7i.-\ 



* The pages referred to in parenthesis are those of the reprint, and not 

 of the original papers. 



Note on the Classification of Certain American Helices. 



t Sucli shells as H. inflecta and //. personata of Europe, referred by 

 Pfeitfer (M.a,\. Blatt., 1835,j to Isognomoitoma, Fitz., 1838, and included 

 by Albers in the genus Ulostoma, do not appear to me to differ from Trio- 

 dopsis, Raf., as the covered umbilicus is scarcely of specific value. I 

 therefore include them in the latter genus, which has priority. 



H. Ilugeli, Shutt, also belongs here. 



Helix elevata, placed by Pfeiffer in Mesodon and by Albers in Triodopsis 

 belongs together with H. Glarkii, Lea, in the genus Xolotrema, Raf. 



H. profunda, placed by Pfeiffer in Ulostoma, together with the species 

 of Triodopsis, is really a Mesodon as Albers has correctly considered it. 



