GASTEROPODA. 187 



FAMILY IV. PLEUROBRANCHID.E. 



Shell limpet-like or concealed, rarely wanting ; mantle or shell covering 

 the back of the animal ; gill lateral, between the mantle-margin and foot ; 

 food vegetable, stomach extremely complicated. 



PLEUROBRANCHUS, Cuvier. 



Ex. P. membranaceus, PI. XIV. fig. 17. Etym. Pleura side, branchia gill. 



Syn. Berthella (plumula) Bl. Oscanius (membr.) Gray. 



Shell internal, large, oblong, flexible, slightly convex, lamellar, with a 

 posterior, subspiral nucleus. 



Animal oblong, convex ; mantle covering the back and sides, papillated, 

 containing spicula ; foot large, separated from the mantle by a groove; gill 

 single, free at the end, placed on the right side between the mantle and foot ; 

 orifices near the base of the gill ; head with 2 grooved tentacles, eyes at their 

 outer bases ; mouth armed with horny jaws and covered by a broad veil with 

 tentacular lobes. 



Distr. 20 sp. S. America, Norway, Brit. Medit. Red Sea. 



Sub-genus ? Pleurobranchaea Meckel; P. Meckelii, Leve, Medit. Syn. 

 Pleurobranchidium (maculaturn) , Uuoy, S. Australia. Mantle-margin very 

 narrow, not concealing the gill ; dorsal tentacles ear -like, oral veil tentaculi- 

 form. 



POSTEROBRANCH.EA, D'Orbigny. 



Type, P. maculata, D'Orb. Coast of Chile. 



Animal shell-less ; oval, depressed, covered by a mantle broader than the 

 foot ; foot oblong, bi-lobed behind ; branchial plume on the left side, pro- 

 jecting posteriorly ; reproductive orifice in front of gill, excretory behind ; 

 proboscis covered by a broad bi-lobed veil ; no dorsal tentacles. 



RUNCINA, (Forbes) Hancock. 



Type, R. Hancocki, Forbes. Syn. ? Pelta, Quatr. (not Beck.) 

 Animal minute, slug-like, with a distinct mantle; eyes sessile on the front 

 part of the mantle ; no tentacles ; gills 3, slightly plumose, placed with the 

 vent on the right side, at the hinder part of the back, beneath the mantle ; 

 gizzard armed ; reproductive organs on the right side. 

 Distr. on Conferva near high-water mark, Torbay. 



UMBRELLA, Chemnitz. Chinese-umbrella shell. 



Type, U. umbellata, PL XIV. fig. 18. Syn. Acardo, Lam. Gastroplax, Bl. 



Shell limpet-like, orbicular, depressed, marked by concentric lines of 

 growth; apex sub-central, oblique, scarcely raised; margins acute; inner 

 surface with a central coloured and striated disk, surrounded by a continuous 

 irregular muscular impression. 



Animal with a very large tuberculated foot, deeply notched in front ; 

 mouth small, proboscidiform, retractile into the pedal notch, covered by a 



