EOTELLA. 147 



and Rotella. The shell partakes of the heavy substance 

 distinctive of the latter^ though smooth on the outer surface^ 

 and, as in Solarium, the umbilicus penetrates inwardly to 

 the apex ; on the other hand, tlie operculum resembles that 

 of Belphinula, with the addition of prominent circular 

 rows of curled flakes ; — a compound shell, which seems to 

 comprise the characteristic peculiarities of its brethren, 

 offering another, amid innumerable instances of that inex- 

 plicable faculty which produces the most extraordinary 

 results by means apparently inadequate. 



The Rotella forms another interesting section of the 

 Trochiis tribe. Small in size, and readily distinguished by 

 its lenticular shape and polished surface, one only, and 

 that of extreme rarity, is otherwise than diminutive, as few 

 exceed half or three-quarters of an inch in diameter. And 

 very curious is the fact, that these polished shells are never 

 found with any extraneous substances attached to them ; 

 a singularity which M. Deshayes believes to indicate some 

 peculiar organization, whereby the mantle of the animal 

 is extended over the shell. 



Who can look upon the Carrier TrocJms without admira- 

 tion? It seems as if the animal occupant was possessed of 

 a powerful cement, which he exudes during the formation 



