ClIAP. VI. THE SUB-GENERA OF ACHATINA. 171 



rather depressed form, but still more by its semicircular 

 aperture, always closed by a horny operculum : the typical 

 species are also peculiar from having a narrow notch, 

 or rather slit, at the base of the outer lip. The 5th 

 and last genus is Cyclostoma, distinguished by its mouth 

 and operculum being perfectly circular ; the margin of 

 the lip is also more or less dilated into a fringe or 

 thickened rim. We shall now take each of these genera, 

 and describe what appear to us the types of form or 

 sub-genera in each. 



(160.) The first and typical genus, Achatina Zam., 

 includes the largest sized sheUs of all those inhabiting 

 the land : they are chiefly found in Africa, where the 

 natives use them as food, and expose them for sale in 

 the markets. The inside of the mouth is sometimes of 

 a brilliant rose-colour, and the outsides of nearly all are 

 elegantly marbled with white ; but, as the epidermis is 

 very tenacious, the ground colour appears olive. The 

 body-whorl of these typical species is large and ventri- 

 cose, the outer lip simple, and the whole shell solid : 

 but in the next type, or Cochlicopa of Ferussac *, the 

 body-whorl is more slender and cylindrical, and the 

 shell is placed very much towards the end of the disk 

 or foot of the animal, which makes this part appear very 

 short : by degrees, however, the spire becomes length- 

 ened, and the body-whorl proportionably smaller ; and 

 in these aberrant species, nearly all of which are longi- 

 tudinally striated, the margin of the outer lip is more 

 sinuated. This elongation of the spire prepares us for 

 the sub-genus Macrospira Guild,, where the spire 

 becomes excessively long and cylindrical ; yet the lip is 

 still very thin, and the pillar is truncated, or notched at 

 the base, precisely as in all the other types. In one or 

 two species we observe, for the first time, a thickened 

 fold in the middle of the pillar, analogous to what is 

 seen in some of the Auriculce and the Ptipce, Now, 



* We adopt M. Fenissac's names whenever they have a right of priority 

 anft are classical ; this group has been called by the strange appellation ot 

 Poli/phemns, as if the animal had not two eyes, but one only I 



