PULMONATA. 61 



Helicidae, and induced M. de Ferussac to arrange the different genera as sub-genera 

 merely of the typical genus Helix. 



The present genus, as defined by Lamarck, embraces considerably more than a 

 thousand living species ; and may well be considered to be " deserving of subdivision, 

 were it only to assist the student in the difficult task of investigation." Very many 

 genera and sub-genera (amounting, including the synonyms, to nearly two hundred,) 

 have, in fact, been proposed from time to time by different authors ; but being 

 nearly all founded, more or less, on conchological differences, they are, with few 

 exceptions, rejected by the advocates of a strictly natural arrangement. M. Deshayes, 

 one of the most able advocates for a system of arrangement dependent on anatomical 

 structure, admits the convenience of having recourse to artificial divisions in this genus 

 in which it is impossible to form natural groups ; and suggests that the Helices may 

 be classed, by the form of the shell, in four sections, consisting of the planorbular 

 species, (Zonites, Montfort; Helicella, Lamarck,) the globose species, (Jcavus, Montfort,) 

 the carinated species, (Iberus, Montfort; Carocolla, Lamarck,) and the trochiform or 

 turbiniform species (Petasia, Beck ; Geotrochus, Swain.) : and that these sections may 

 be again subdivided into groups, according as the species are or are not umbilicated, 

 have the aperture simple or reflected, or are or are not furnished with teeth. 



The fossil Helices are more numerous than might be expected with respect to land- 

 shells. Many extinct species, from the Freshwater deposits of the Paris basin, 

 have been described by MM. Brogniart, ('Ann. du Mus.' vol. xv, p. 378,) Deshayes, 

 (' Descr. des Coq. Foss.,' &c, vol. ii,) Matheron, ( c Ann. des Sci. et de lTndust. du 

 Midi,' vol. hi,) Michaud, ('Guerin's Mag. de Zool.,' 1837,) De Roissy, (' Guerin's Mag. 

 de Zool.,' 1839,') and Melleville, ('Mem. sur les Sables Tert. Inferieurs du Bassin de 

 Paris,' p. 45 ;) and from the contemporaneous Freshwater formations in Germany by 

 MM. Zeiten, (' Petr. Wurt.,' tab. xxix and xxxi,) Steininger, ('Bull. Soc. Geol. de 

 France,' vol. vi,) Deshayes, ('Ency. Method. Vers.,) and Pusch, (' Polens. Pal./ p. 94.) 

 One species only, H. globosa, has as yet been described from the synchronous deposits 

 in England ; to this I am enabled to add eight species, one of which is identical with 

 an existing species, H. labyrinthica, Say., found in North America. 



Many species also occur, mixed with marine remains in the Miocene formations of 

 Touraine, Dax, and Bordeaux, and in the Pleiocene formations of Piedmont, the Crag 

 of England, and its equivalent in Belgium ; of these but few are extinct, by far the 

 greater number being referred to existing species. 



Among the French species described by M. Deshayes is one (//. dubid), which, on 

 the authority of Mr. Underwood, is mentioned as occurring in the Isle of Wight. I 

 have not met with any specimen from that place ; and M. Deshayes, as I learn from 

 that gentleman himself, entertaining doubts as to the English locality, I have not 

 considered H. dubia as an English species. 



