184 



SHELLS AND SHELL-FISH. 



PART 



Analogies of the Genera Clausilia and Pupa. 



Sub-genera of 

 Pupa. 



Siphonostotna. 

 Megaspira. 



Gonospira. 



Pupa. 

 Plicadomus. 



Sub-genera of 

 Clausilia. 



Analogies. 



f Spire exceedingly long, the upper 7 



i portion deciduous. 3 



C Spire greatly lengthened, the up- 7 



l per portion persistent. 3 



Spire moderate, with few whorls, 'J 



the tip thick and obtuse ; the f 



aperture generally without T 



teeth. ) 



Spire moderate, but with manyi 



whorls of nearly equal thick- >• 



ness 3 



Clausilia. 



Pupella. 



and broadly margined 



(170.) Our next genus is Helicina, — a group of 

 remarkable shells, of which, as near forty species are now 

 known, the sub-genera may be advantageously charac- 

 terised. This will be done in our systematic arrange- 

 ment, and in the mean time a few general remarks is all 

 that we can here insert. They are small helix-formed 

 shells, distinguished by their semilunate aperture, which 

 is closed by an operculum. We have not seen, as yet, 

 any intermediate form which renders the passage between 

 them and the last genus sufficiently clear. The animal, 

 as seen in H. occidentalis (Jig. 28.), has been well drawn 

 by Guildingj it has only two tentacula, with the eyes 



at the base. In this respect the Helicin<je, as Cuvier 

 observes, have a close affinity with the CyclostomcB, 

 many of which are also turbinated shells, and all are 



* I should conceive, theoretically and analogically, that Balia would 

 represent Gonospira by its toothless aperture ; and that the prototype of 

 Megaspira would be perfectly like Clausilia, but without any teeth or 

 folds, and the spire (probably) persistent. 



