100 . MOLLUSCA. 
® 19. Conus.—This genus is so very natural, that it has 
undergone no changes since the days of Linnzus, except by 
the addition of new species. That author was acquainted 
with thirty-five species and a few varieties; but M. Hawss 
communicated to Bruguiére descriptions of one hundred and 
forty-six, from specimens existing in his own cabinet. We 
cannot boast of any British species. 
20. Crprma.—This genus is equally natural as the for- 
mer. It has undergone no change since the days of Major. 
21. Buria.—This genus presents to the mere conchologist 
a source of great perplexity. It displaysat once the absurdity 
of dividing the molluscous animals into testaceous and naked, 
since no such distinctionis observable in nature. Many of 
the shells which were formerly included in this genus are 
found to be contained within the common integuments of 
the animal. It was this circumstance which induced Lin- 
neeus to separate the limax and the aplysia from the vermes 
testacea. Both of these have shells, but they are concealed. 
In imitation of the same principle, Lamark has formed a new 
genus among the naked mollusca, called Butuma, for the 
reception of those bullz in which the shell is concealed. 
The bulla aperta is the type of the genus. The bulla plu- 
mula of Montagu is another shell included in the animal, 
which is very closely connected with the genus Pleuro- 
branchia of Cuvier. (Annales du Mus. v. 269). It may be 
asked, are all the other bulle found in similar situations, and 
consequently do they belong to the naked mollusca? La- 
mark considers, and apparently with reason, that all those 
which are distinctly spirally involuted, and ornamented with 
colours, are not entirely inclosed in the cloak of the animal, 
and ought therefore to be ranged with the testaceous mol- 
lusca. How few British species does this character include. 
