322 MANUAL OF THE MOLLUSCA. 
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 martle 
lobe. 
Distribution, 7 species. Mediterranean, Red Sea. 
IcARuS, Forbes, 1843. 
Type, I. Gravesii, F. 
Synonym, Lophocercus (Sieboldtiu) Krohn, 1847. 
Shell like Bulleea; 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. 
LopicER, Krohn. 
Type, Lu. Philippu, Pl. XIV., Fig. 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. 
FamiIty LVY.—PLEUROBRANCHIDA. 
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, OCuyier. 
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 conyex. 
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 
