38 



ON CLASSIFICATION. 



dium, and metcvpodium ;* while the Aphjsise, in which the foot 

 proper has the ordinary composition, exhibit processes from the 

 lateral and upper surfaces of that organ, having the form of 

 great muscular lobes, which serve as a sort of aquatic wings to 

 some sj^ecies, and are termed epipodia. 



The Br anchiog aster opoda are such of the Gasteropoda of 

 Cuvier as breathe water either by means of the thin wall of the 

 mantle cavity [Atlanta, e.g.), or by special pallial branchiae 

 (Peethiibranchiata, Tectibranchiata, &c), or by certain parts of 

 the integument of the body (Nudibranchiata) more or less 



Fie. 15. 



15. — Diagram exhibiting the disposition of the intestine, nervous system, &c, in a 

 common snail (Helix), a, mouth ; b, tooth ; c, odontophore ; d, gullet ; e, its dilata- 

 tion into a sort of crop; /, stomach ; g, coiled termination of the visceral mass; the 

 letter is also close to the commencement of the intestine, which will be seen to lie 

 "ruler the oesophagus, and not over it as in the whelk ; h, rectum ; *, anus : k, renal 

 sac; I, heart; m, lung, or modified pallial chamber; n, its external aperture; o, 

 thick edge of the mantle united with the sides of the body; p, foot; r, cerebral, 

 pedal, and parieto-splanchnic ganglia aggregated round the gullet. 



specially modified. The next class, the Pulmogasterofoda,! 

 on the other hand, are the Pulmonate Gasteropoda of Cuvier, 



* I proposed these terms in a Memoir in the " Morphology of the Cephalous 

 M"llusca," published in the Phdozopldcal Transactions for 1853. 



i I adopt these convenient names at the suggestion of my friend Profe.—< ( i 

 Greene, of Queen's College, Cork. 



