CHAP. III. TRIBES OF THE GASTEROPODA. 55 



places such genera as Planorhis and Ampullaria in two 

 different orders, merely on account of a difference in their 

 organs of respiration, he falls into as great an error as 

 that he has elsewhere committed in uniting the Cyclo- 

 .hranchia to his Acephala. The order Piihnonaria, there- 

 fore, must be clearly abolished. This, indeed, has been 

 already done by Lamarck, whose authority on all ques- 

 tions of natural affinity must, in general, be regarded as 

 superior to that of Cuvier. 



(46.) ^\^ith the foregoing restrictions, the primary 

 divisions of the order before us wuU be found to consist 

 of the five following tribes: — 1. The Zoophaga of 

 Lamarck, or the carnivorous shell-fish (corresponding to 

 the Pectinibranchia Cuv.); 2. The Phytophaga of the 

 same author, which live chiefly on vegetables, as the 

 snails and slugs; 3. The Scutibranchia Cuv., or lim- 

 pets ; 4. The Cyclobranchia Cuv., or chitons ; and, 5. 

 The Tectibranchia Cuv., or buUas, whose univalve 

 shells, where they exist, are all hid in the flesh of the 

 animal, while their mantle is dilated into two fin-Hke 

 lobes, with which they can swim. We shall now state a 

 few general particulars of these tribes, and then proceed 

 to determine their analogies. 



(47.) The Zoophaga are the most pre-eminently 

 typical of the whole of the testaceous Mollusca ; and 

 this holds good, whether we regard the organisation of 

 the animal, or the symmetry and beauty of their ex- 

 ternal shell, wdth which, in every instance, they are 

 provided. They have only two tentacula ; and the eyes, 

 which are always conspicuous, are sometimes (as in the 

 Stromhid(E) highly developed- The edge of the mantle 

 is almost always provided with a siphon, or tube for 

 respiration, and by which the animal can breathe without 

 protruding its head and foot from the aperture of its 

 shell : this siphon is protected by a corresponding canal, 

 either long or short, at the base of its habitation ; and its 

 presence, in all these Mollusca, constitutes one of their 

 most essential characters. The mouth, also, is very re- 

 markable, — resembling more or less, as Cuvier well 



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