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LETTER XIX. 



THE PHYTIVOROUS MOLLUSCA. 



The herbivorous, or, as they are frequently named, the 

 phytophagous mollusca, belong exclusively to the class of 

 Gasteropods, and embrace, with few exceptions, the Pul- 

 mones, about half of the Nudibranches, the Inferobranches, 

 a great proportion of the Tectibranches, the Scutibranches, 

 and Cyclobranches, and such of the Pectinibranches as have 

 no slit or siphon in the collar of the mantle, or, which is the 

 same thing, whose shell has an entire aperture.* The 

 mouth of the animal is not elongated into a proboscis, but 

 is furnished with two jaws ; and the tongue is usually broad 

 and membranous, although sometimes long and filiform. 

 What proportion these herbivorous tribes united may bear 

 to the zoophagous, I am not prepared to say, for we are not 

 in possession of a complete catalogue of the species ; but 

 to make a conjectural approximation to the solution of this 

 question, let us assume that the enumeration of the species 

 given by Lamarck is equally defective in all the families, 

 (and I know of no fairer mode of coming at the truth,) 

 when we shall find that the phytivorous are fewer by a third 

 than the zoophagous, — so that Meckel errs in asserting 

 that the great bulk of the Gasteropods live on vegetable 

 matters : — 



ZOOniAGOUS. 



Nudibranches 

 Bulleens 

 Testacellus 

 lantliina 

 Naticfe 

 Canaliferes . 

 Ailees 



Purpuriferes . 

 Scalariens . 

 Columellaires 

 Enroulees 

 Heteropodes . 



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* That is to say, the families Trochoides and Capuloides of Cuvier, Reg. 



