l68 SHELLS AND SHELL-FISH. PART 1. 



be observed, that in the strongly sculptured ridges of 

 most of the species, a nearer approach is made to the 

 coronated Geomitra (fig. 20.), than to any other land 

 shell. The last sub-genus to be noticed was long 

 ago characterised by the masterly pen and pencil of 

 Guilding, but seemingly overlooked by our concholo- 

 gists ; it is his Siphonostoma *, and is distinguished at 

 once both by the animal and its shell (*S'. costata Guild., 

 fig. 22.). The foot is remarkably short, while the 

 spire of the shell is deci- 

 duous, i. e. falling off soon 

 after it has reached matu- 

 rity ; sometimes, indeed, the 

 animal has been captured 

 before this process takes 

 place : the shell is then re- 

 markably beautiful, exhibiting as many whorls as Macro- 

 spira, but with this difference, that the upper portion is 

 gradually attenuated to a fine point : this type is thus 

 separated from Macrospira, not only by its decidu- 

 ous spire, but by its round aperture and its thickened 

 lips, which gives it all the aspect of a Cpclostoma, 

 except that the margin of the lips, in some species, is 

 even detached from the body-whorl. That there will 

 be intervening modifications between each of these sub- 

 genera, so that they may be blended more harmoniously 

 together, can admit of little doubt : our only regret is, 

 at present, that they are too strongly marked and dis- 

 tinct ; nevertheless, we may feel confident, after studying 

 the annexed table, that these forms foUow each other in 

 the order in which they are now placed. We insert in 

 this place the series of the Clausilitr, which represent 

 Pupa, in order to show the intimate relations of the 

 two groups j but we shall subsequently return to that 

 genus, because it forms part of the sub-family Acha- 

 tints. 



* Guilding imposed this name after he had discovered that Brachijius 

 had been used by us to designate a group of birds. 



