74 EOCENE MOLLUSCA. 



smooth, inflected and truncated at its base, forming a slight notch where it joins the 

 outer lip. 



The third division made by Bruguiere in his genus Bulimus, consisting of those 

 species in which the columella is truncated at the base, was formed by Lamarck 

 into the present genus. From this Montfort withdrew his genera Liguus, {Chersina, 

 Humph.,) consisting of the conical forms in which the aperture is short and nearly 

 round ; and Polyphemus, comprising the oblong sub-turreted species, with an un- 

 dulating outer lip, to which Bolten had already given the name Oleacina, and which 

 forms the genus Glandina of Schumacher and Say, and the sub-genus Cochlicopa of 

 Ferussac. 



As some of the Bulimi present a sharp outer lip, the truncation of the columella 

 appears to be the only character by which the Achatinae can be separated from that 

 genus, and the value of this character must depend on its being the result of some 

 peculiarity of generic importance in the organisation of the animal. M. De Blainville 

 states that he has observed in the animal of Acliatina zebra an interruption in the collar 

 where the two sides unite, as if caused by the exsertion (saillie) of the columellar 

 muscle, and to this he attributes the truncation of the columella ; but, according to 

 Ferussac, this truncation is not the result of any peculiar organisation, as is the case 

 in other molluscous animals, the columella of whose shells present this character ; and 

 that author therefore unites the Achatinae to his genus Helix, of which they form the 

 sub-genus Cochlitoma ; and M. Deshayes, on account of the similarity of organisation 

 presented by the animals of Bulimus and Achatina, proposes to re-unite Achatina 

 with Bulimus. The genus, however, is very generally adopted as well by English as 

 by foreign Malacologists, and I have therefore retained it. 



The subdivisions proposed by Bolten and Montfort depend on the proportions 

 and other characters in the shell, of trifling importance, which are generally considered 

 as insufficient for generic distinction, however useful they may be for the division of 

 a genus into sections. The recent species A. glans, and the cognate species which 

 form the genus Glandina, are confined to the West Indian Islands, and the adjacent 

 parts of the American Continent ; and the peculiar form of the outer lip may be 

 used with convenience, as one of the indications of the limits of geographical dis- 

 tribution of species. 



The Achatinae are generally large shells ; some, in fact, attain a greater size than 

 any other land shells at present known, and many are covered with an epidermis. 

 Although generally dextral, they are in some species constantly sinistral. They are 

 found chiefly in tropical climates, and, according to Blainville, in marshy lands. Some 

 few are European, but only one or two small species occur in England. One fossil 

 species {A. pellucidd) has been described by M. Deshayes from Parnes ; and Bouillett, 

 in his catalogue of the fossil shells of Auvergne, has given another species, which he 

 refers to the recent A. acicula (Lamarck). 



