292 HELICID^E. 



which revolves within the aperture ; and its base is more 

 or less truncated, so as to form a basal notch. Oper- 

 culum, none. 



GEOGRAPHICAL DISTRIBUTION. This is a tropical, 

 and, properly speaking, an African genus, all the typical 

 species being obtained from that continent or the neigh- 

 borhood. Some of the aberrant forms of the Lamarckian 

 genus are found elsewhere ; as on the European coast of 

 the Mediterranean, at the Sandwich Islands, at the West 

 India Islands, etc. 



REMARKS. The genus as characterized by Lamarck, 

 included shells of widely different natural characters. 

 The typical species differ from Bulimus merely by the 

 truncation of the columella ; and this varies in degree 

 till we come to species on the boundaries of either 

 genus. The aberrant groups have been, more recently, 

 withdrawn from the genus, under the names Glandina, 

 Achatinella, Tornatellina, etc., which are now regarded 

 as generically distinct. Bulimus fasciatus has usually 

 been placed under this genus, and is a fair example of 

 the inosculation of the genera Achatina and Bulimus. 

 The truncation of the columella, which is the grand mark 

 of distinction, is sometimes very decided, and at others 

 is nearly imperceptible. The tw r o shells which have been 

 placed under this genus in the first part of this work, 

 might with more propriety be arranged elsewhere ; and 

 we shall therefore not dwell further on the various modi- 

 fications of the genus, but reserve further observations 

 for the special descriptions. [G.] 



