34 SHELLS AND SHELL-FISH. PART I. 



coasts ; but a still greater assemblage are carnivorous, — 

 devouring not only living, but dead, animals, and even 

 attacking other tribes of their own class. It would be 

 interesting to know in what manner nature has pro- 

 vided for the sustenance of such as are permanently- 

 affixed to one spot. Some of these have divers me- 

 thods of exciting little currents in the water, by which 

 means fresh portions of it are brought to the mouth, 

 along with which such minute animals or fragments of 

 vegetables as are adapted for food are secured. The 

 branchipodous bivalves, like the Terehratidce, although 

 sedentary, are provided with long fringed processes, 

 which are, no doubt, employed to capture their prey, 

 in a similar manner to the arms of the CirripedeSj or 

 barnacles; while the cuttlefish (^Cephalopoda) and the 

 Tritojiia swim about in search of marine animals 

 weaker than themselves. In regard to their geographic 

 distribution, much might be said, did we not fear 

 being drawn into longer details than our space would 

 permit. It will be only necessary to observe in this 

 place, that the geographic range of the Testacea is not 

 so wide or uncircumscribed as the generality of authors 

 assert. Tropical latitudes, as usual, display a greater 

 variety of species, and a larger number of individuals, 

 than those seas which lie under temperate or frigid 

 skies. The Testacea of Europe are as distinct from 

 those of America, as the latter are from those of Aus- 

 tralia, Africa, or Asia. "\V^e have already illustrated 

 this fact in that part of our series devoted to the geo- 

 graphic distribution of animals ; and it may be safely 

 asserted that the grand features of zoological geography 

 are as conspicuous in this class of animals, as in any 

 other. 



(29.) The great natural divisions of the testaceous 

 Mollusca appear to us to be these : — The fii'st, or 

 pre-eminently typical, are unquestionably the Gastero- 

 poda, or spiral univalves, whether we consider the 

 comparative perfection of their internal or their external 

 structure. The second, or sub-typical class, is com- 



