414 



MOLLUSCA. 



...-5 



3- 



Fam. 3. Limapontiidae. Without lateral expansions or cerata. Anus 

 median postero- dorsal. Liver but little branched. Limapontia Johnston ; 

 Actaeonia Quatref. 



The position of the Bhodopidae is uncertain : they are planarian-like naked 



forms, without branchiae, ten- 

 tacles, buccal mass, or radula. 

 Recently it has been shown* 

 that the larva of this form is 

 6 without a shell ; thus destroying 



the main reason for regarding it 

 as a nudibranch mollusc. 



Sub : order 2. Pulmonata. 



Euthyneura in which the 

 pallial-cavity is modified as 

 a lung, and is without a 

 ctenidium. Tlie opening of 

 the pallial-cavity is small. 



The pallial-cavity is often 

 reduced, as well as the shell. 

 Sometimes the shell is in- 

 ternal or absent. There is 

 never an operculum in the 

 adult except in Amphibola 

 (it is present in the young 

 stages of Auricula, Siphon- 

 aria, Gadinid). The roof 

 of the mantle-cavity is pro- 

 vided with a network of 

 vessels for aerial respiration, 



and the mantle-cavity constitutes a lung. In Vaginulus, Peronia, and 

 Onchidium the lung is absent in consequence of the almost complete 

 disappearance of the mantle-cavity. In some cases the lung may 

 be filled with water and serve for aquatic respiration (Siphonaria, 

 some Limnaea and Planorbis). The auricle is usually in front of 

 the ventricle. The kidney has usually a more or less elongated 

 duct (ureter). 



The opening of the pallial-cavity is reduced to a pore placed on 

 the right side. The anus and renal openings are placed near the 

 opening of the lung (in Auricula alone does the anus open in the 



FIG. 331. PleuropJiyllidia lineata, ventral view 

 (from Lang, after Souleyet). 1 genital opening; 

 2 branchial processes ; 3 anus ; k pedal gland ; 

 5 mouth 6 tentacle shield ; 7 foot. 



* S. Trichinese, "Nuove osservationi s. Rhodope Veranii" Rend. Accad. 

 Napoli (2), vol. 1., p. 131. See also L. Bohmig in Z. f. w. Z., 56. 



