322 MANT7AI OF THE MOLLrSCA. 



Animal shell-less, ornamented ■with filaments, sometimes 

 dendritic, foot narrow, lateral crests united, leaving only a 

 narrow branchial slit ; gills not covered by an opercular mantle 

 lobe. 



Distribution, 1 species. Mediterranean, Eed Sea. 



Icarus, Forbes, 1843. 



Tyjpe, I. Gravesii, F. 



Synonym, LopJiocercus (Sieboldtii) Krohn, 184*7. 



Shell like Bullcea ; convoluted, thin, ovate, covered with 

 epidermis, outer lip separated at the suture, posterior angle 

 inflected and rounded. 



Animal slender, papillose ; tentacles 2, ear-shaped ; eyes 

 sessile on sides of head ; side-lobes reflected and partly covering 

 the shell, united behind ; tail long and pointed. 



LOBIGER, Krohn. 



Ttjpe, L. Philippii, PI. XIY., Pig. 16. Sicily. 



Shell oval, transparent, flexible, slightly convoluted ; covered 

 with epidermis. 



Animal slender, papillose, with two flattened, oval tentacles, 

 and minute sessile eyes on the sides of the head ; shell exposed 

 on the middle of the back, covering the plume-like gill ; sides 

 with two pairs of rounded, dilated lobes, or natatory appendages, 

 foot linear, tail long and slender. 



Distribution, 4 species. Atlantic ; South Europe. 



Family IV. — Pleurobranchid^. 



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. 



Pleurobran'CHIJS, Cuvier. 



Example, P. membranaceus, PL XIV., Fig. 17. 



Etymology, pleura, side, branchia, gill. 



Synonyms, Berthella (plumula), Bl. Oscanius (membr.). Gray. 



Shell internal, large, oblong, flexible, slightly convex, 

 lamellar, with a posterior, sub-spiral 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 



