128 



SHELLS AND SHELL-FISH. 



upper plaits of the pillar, in almost all, are larger than 

 the lower; and the general form of the shell is equally 

 or unequally fusiform. It is almost impossible to esti- 



mate the number of species, as new ones are constantly 

 coming to light ; but there probably exists already, in our 

 cabinets, about two hundred and fifty, of which more 

 than forty were brought home by Mr. Cummin from 

 the western coast of Tropical America. We suspect, 

 from these data, that, in a few years, the increase of 

 known species will come near to 300, leaving out those 

 that belong to the three aberrant genera — Mitrella, 

 ConoBhelhr, and Mitreola. Nearly all these are excluded 

 from the European seas ; and, what is still more extra- 

 ordinary, not more than half a dozen can be called com- 

 mon shells. This scarcity of mitres certainly does not 

 originate from the difficulty of gaining access to their 

 haunts ; for, although some are known to live at great 

 depths*, yet both i\IM. Stuchbury and Cummin inform 

 us that they generally found these shell-fish in shallow 

 water, near coral reefs. Hence we conjecture that their 

 chief metropolis must be the great Pacific Ocean, where, 

 among tlie countless numbers of existing islands, and 

 the coral foundations of others, the number of species 

 now unknown may be nearly equal to those already 

 described. The animals of a very few have been pub- 

 lished by M. Quoy, in the invaluable plates of his 

 voyage; for the particulars of which we have not suffi- 

 cient space. 



(118.) The primary divisions of the whole of the 

 family, as already intimated, correspond with those of 



* As Mitra zonata, which. Dr. Leach says, was fished up out of very 

 deep water near Nice. 



