32 LEPAS. 



and minor. They in fact differ merely in the situation 

 of the rings, which in some shells, as fig. 3, are farther 

 apart than in others, and the shell is occasionally some- 

 what larger. 



These curious productions inhabit the back of the 

 South Sea whale, where they bury themselves in the 

 skin and fat. Dufresne, in a memoir which is a 

 continuation of that of Lamark, observes that the 

 animal, independent of its other parts, is furnished 

 with a collar lightly striated, which secretes the 

 testaceous matter for the formation of the rings. This 

 collar, always remains visible between the sides of the 

 shell and the operculum, see fig. 1. In proportion as 

 new rings are formed, the animal buries its shell 

 deeper in the fat of the whale, insomuch that two rings 

 are all that are at any time visible above the skin$'the 

 rest of the shell being firmly secured in its situation by 

 the help of its annulated surface. The animal when 

 it projects above the operculum shows a fleshy neck, 

 through which proceed the tentacula. This neck is 

 seen in fig. 2. These shells are generally about an inch 

 long, but as their growth is progressive, depending upon 

 their age, they have been found of three times the usual 

 length. A group of them is represented at fig. 2, to 

 show their natural situation in the whale. 



The fine specimens of this shell, for which the author 

 is indebted to Dr. Coombe, were not procured till after 

 plate 4 was printed : it has therefore been necessary to 

 distinguish this plate by an asterisk, as it must be 

 placed, in order, at the head of the genus. 





