311 



ture, which is thin, papyraceous, very fragile, and semi- 

 transparent. The shell of the C. vitrea is in the form 

 of a fool's cap, flattened at the sides, the summit spiral- 

 ly recurved towards the aperture, but never entering it. 

 It has one keel only on the whole length of the back t 

 sharp, and dentated: the animal inhabiting it is never 

 quite inclosed by the shell, which only serves to pro- 

 tect certain parts of its body. An example of this 

 shell, which is considered by collectors the most rare 

 of all the Testacege, exists in the cabinet of the Earl 

 of Mountnorris, and is supposed to be the only one 

 in this country. Another is in the French Museum. 



The next species described by Lamarck, the C. 

 fragilis, (Ency. Method, pi. 444,/. 3), is much small- 

 er than the preceding, and may be distinguished 

 from it by the very fine longitudinal stria?, diverging 

 from the summit to the margin ; it also has no dorsal 

 carination. 



The third species, C. cymbium, (Martini 1, t. 18, 

 f. 16 1, 162), is not larger than a grain of sand, and can 

 only be seen through a magnifying glass. 



Carinaria vitrea Carinaria fragilis 



Carinaria cymbium. 



