10 



CLASSIFICATION OF GASTEROPODA 



sexes are united in the same individual. The Ojnsthohrcmchiata 

 fall into two divisions : (a) Tectihranchiata, in which the In-eathing 

 organ is more or less covered l)^ the mantle, and a shell is 

 usually present, which is sometimes rudimentary, e.g. Bulla, 



i^MMa 



Fig. 5.— a, A Tectibrau- 

 chiate Oi)isthobrauch, 

 Umlirella m editerra- 

 nca Lam., Naj^les : a, 

 anus ; br, brauchia ; /, 

 foot ; VI, mouth ; rh, 

 liiiuopliores ; sh, shell. 



B, A Pteroi^od, Jlya- 

 laea tridentata Forsk., 

 Naples : sh, shell ; I, I, 

 swimming lobes of foot. 



C, A Nudibranchi- 

 ate Opisthobranch, Ae- 

 olis iMTcgrina, Naples : 



f, foot ; c, cerata. 



Aplysia, Umhrella, and the whole group of PteroiJoda ; (h) JVudi- 

 hranchiata, or sea slugs, which have no shell and no true 

 ctenidia, but breathe either by the skin, or l;)y ' cerata ' or 

 papilliform organs prominently developed on the back : e.g. 

 Boris, Aeolis, Dendronotus. 



(4) The Pulmonata ^ are asymmetrical air-breathing non- 



FiG. 6. — Examples of — A, Pulmonata Basommatophora, the common Limnaea 

 peregra Miill. : e, e, eyes ; t, t, tentacles. B, Pulmonata Stylommatoiihora, 

 Helix hortensis Miill. : e, e, eyes ; t, t, tentacles ; 2^- o, pulmonary orifice (the 

 position of the pulmonary orifice in Limnaea will be seen by reference to 

 Fig. 101). 



marine Mollusca, generally, but not always, furnished with a 

 shell. The sexes are always united in the same individual, and 

 the operculum is always wanting, except in Amphihola. They 



^ P'ulmo, a lunff. 



