CHAP. III. THE CARNIVOROUS TRIBE. , 6l 



the PlanaridcE among the Parenchymata are naked 

 chitons (^Cijclohranchia). The Cephalopoda, in hke 

 manner, are as perfectly represented by the swimming 

 tribe of the Tectihranchia ; and like them, also, have 

 their shell internal. Adverting, again, to the two first 

 analogies, we find the primary types, the Zoophaga and 

 the Dithyra, furnished with long siphons^ or tubes, 

 which are totally wanting in the secondary types. To 

 this table^ however, w^e may hereafter return ; and, in 

 the mean time^ w^e shall enter at once on the most 

 typical families of the entire class. 



\5S.^ The tribe of the Zoophaga, or rapacious shell- 

 fish, is distinguished by a tubular or proboscis-like 

 mouth, a respiratory siphon, and two tentacula, upon the 

 sides or near the base of which are the eyes. In some 

 few, as in the cowries (^Cypr(Ea\ the mantle is ex- 

 ternal, and almost envelopes the shell ; and this, we sus- 

 pect, is likewise the case in some of the Volutidcs, or 

 volutes ; but in general it is internal, and of ordinary 

 dimensions. Nearly all are provided with a horny oper- 

 culum for closing the aperture of their shell ; but in the 

 Cones and ColumheUirKe this is reduced to a mere 

 vestige ; while in the Cypraidce, and such as have the 

 lobes of the mantle very much developed, it is unneces- 

 sary, and therefore does not exist. All these variations, 

 however, in the operculum are slight and trivial, in com- 

 parison to those exhibited in the form of the animal 

 and the construction of the shell. Here the greatest 

 variety, and the most regular constancy in the variation 

 of natural groups, is everywhere discernible. Hence it 

 is, that while our primary attention must be directed to 

 the variation of the animal, we must still have a suf- 

 ficient regard to its testaceous covering. It is the abuse, 

 and not the judicious use, of a regard to the shell, which 

 is to be condemned. A system built only on the vari- 

 ation of the animal, would be as useless and insufficient 

 for all practical or philosophic purposes, as another 

 would be detrimental to sound principles of classifi- 

 cation, if it w^as framed entirely on the form of the 



