HELICIDJE. 119 



on the right side. Shell imperforated ; spire de- 

 pressed, of only a few whorles; mouth large, 

 rounded, lunate ; peristome thin. 



This genus is intermediate in form between a slug 

 and a snail, having the shield-like mantle of the one, 

 and the globular external shell of the other genus. 

 The shells are very like the Zonites in their appearance, 

 but have a much smaller and more depressed spire, 

 more rapidly enlarging whorles, and a much larger 

 mouth ; but they are best known by their axis being 

 imperforated. 



Nilson observes, that many zoologists, especially the 

 French ones, contend that the animal cannot with- 

 draw itself into its shell : he has observed this species 

 not only withdraw itself entirely, but so much so as to 

 leave a space behind it like the snails. [Moll. Suec, ii.) 



Nilson kept some specimens, which he had caught 

 at the end of January, in a bell glass, and on the 19 th 

 of February he observed some eggs placed among the 

 putrescent leaves. The eggs were oval, globose, white, 

 subpellucid, with a central opake spot, and placed in 

 little tufts, consisting of eight or nine eggs. In the 

 beginning of March the opake spot was not increased 

 in size, but showed signs of slow movement, and on the 

 21st or 22d of March the animals were excluded. He 

 thought, when he observed them with the microscope, 

 that the animal bored its way through the egg-shell, 

 forming a hole out of which first the head, and then 

 the foot, was produced. When first hatched, both the 

 animal and shell were perfectly formed, but the eyes 

 were retracted into the body ; they are afterwards pro- 

 truded. 



