CHAP. VI. ANALOGIES OF THE ACHATIN^E. 



173 



observed in young shells; and even in those which 

 are adult it is very slight, yet it is distinguishable. 

 In the typical Achatinte, on the contrary, the base of 

 the pillar is turned outwards, the mouth is not ob- 

 lique, and the whole of the outer lip is so thin and 

 fragile, that it breaks on the slightest touch : a more 

 intimate union, in short, cannot possibly exist. 



(l6l.) Having now, to all appearance, closed the 

 circle of Achatina, we may compare it with the primary 

 divisions or genera of this sub-family. 



Analogies of the sub-genera of ACHATINA. 



Sub-genera. 

 Achatina. 

 Cochlicopa. 



Macrospira. 



Leucostoma ?. 

 Achatindla. 



Analogical Characters. 



("Large; ventricose; strictly typi- > 

 I cal $ 



f Body- whorl more contracted ; 7 

 i spire more lengthened. 3 



'Shell cylindric; spire exces--) 

 long ; the body-whorl f 

 aperture short, nearly f 



r Outer lip with a distinct notch at } 

 1 the base ; inner lip not thick- > 

 C ened internally. j 



f Lip thickened ; aperture nearly 7 

 round. J 



r Shell cy 

 J sively 

 1 small ; 

 (. round. 



Genera of the 

 Aehatinte. 



ACHATIWA. 

 BULIMUS, 



CLAUSILIA, 



HELICINA. 

 CYCLOSTOMA, 



This result of following the course of affinities is im- 

 portant, as showing that the modifications of the spiral 

 snails are regulated on a uniform and a very simple 

 system. The more experienced zoologist need hardly be 

 reminded, that, in comparing Cochlicopa with Bulimus, 

 we institute the comparison with that division of the 

 latter genus which is sub-typical, because Cochlicopa 

 is also sub-typical : in both these the spire is as long, 

 and generally longer, than the body- whorl ; whereas in 

 the pre-eminently typical Achatince and Bulimi, the 

 body- whorl is ventricose, and the four whorls of the spire 

 short. So beautifully do the greater part of these five 

 sub-genera of Achatina blend and pass into each other, 

 that it is no easy matter to determine where one ends 



