CHAP. VI. HELICID^. BULIMUS. 177 



exhibits the typical perfection of this form : but there 

 are others, much smaller, where the outer lip is thin ; 

 and these are the connecting links between this and 

 Macrospirn. The well-known Helijc decollatus Linn, 

 seems to belong to this sub-genus, and conducts us im- 

 mediately to Bulimulas of Leach. We now come to 

 shells of the ordinary shape ; the outer lip is rather thin 

 or scarcely reflected, and the inner so little developed 

 tliat it merely forms a thin plate over the umbilicus, 

 where this latter exists. Before we had sufficiently 

 analysed this family, we were little disposed to adopt 

 this sub-genus. Its characters are so very slight, and 

 the greater or lesser reflection of the outer lip is so 

 variable, that we did not think such considerations alone 

 were sufficient to authorise the separation of these shells 

 irova BuUmus: more particularly as the exquisite draw- 

 ings of Guilding did not show any outward difference in 

 their animals. But no sooner had it become evident to 

 us that Bulimulus, in fact, was the representative not 

 only of Zonites, but of Achatina, than the full value of 

 the distinction became manifest. There are not many 

 sectional forms among these shells, which are all rather 

 of a small size; but some, as the Bulimulus undulatus, 

 Antiguensis, and Proteus Guild., are very elegant. The 

 third sub-genus, or Bulimus proper, is a very numerous 

 one. The fact is, that, being the pre-eminent type of 

 all these sub-genera, it contains representations of all, 

 and under more modifications than are found in Acha- 

 tina proper. As we shall return to these 

 shells subsequently, we may now pass 

 on to Auricula, the fourth sub-genus, 

 which, with the general form of Buli- 

 mus^ although less ventricose, unites the 

 peculiar character of having one, or 

 sometimes two, plaits on the pillar near 

 the base of the aperture. The next 

 genus, hitherto overlooked, is Gonyo- 

 stoma {fig. 25.), represented by the Bit- 

 lirnus of that name. The length of its spire, and the 



