a GASTEROPODA. 256 
- Shells extremely like the recent phorus, are met with even in 
_ the carb. limestone and has. 
Lacuna, Turton. 
Etymology, lacuna, a fissure. 
Type, L. pallidula (Pl. [X., Fig. 16). 
Synonym, Medoria, Gray. 
Shell turbinated, thin; aperture semi-lunar; columella flat- 
tened, with an umbilical fissure; operculum pauci-spiral. 
Animal ; operculigerous lobe furnished with lateral wings and 
tentacular filaments. Teeth 5 cusped; uncini 1, 2, dentated, 
3 simple. Spawn (ootheca) yermiform, thick, semi-circular. 
Range, low water—s0 fathoms. 
Distribution, 16 species. Northern shores, Norway, Britain, 
Spain. 
fossil, 1 species. Glacial beds, Scotland. 
LiriopaA, Rang. 
Litymology, litos, simple, ope, aperture. 
Type, Li. bombyx (Pl. IX., Fig. 24). 
Shell minute, pointed; aperture slightly notched in front ; 
outer lip simple, thin ; inner lip reflected; operculum spiral. 
Distribution, 6 species. Atlantic and Mediterranean, on float- 
ing sea-weed, to which they adhere by threads. 
Fossil, 1 species. Pliocene (Crag). 
Rissoa, Frémenyille. 
Etymology, named after Risso,* a French zoologist. 
Type, R. labiosa (Pl. [X., Fig. 17). 
Synonym, Cingula, Flem. 
Shell minute, white or horny; conical, pointed, many-whorled; 
smooth, ribbed, or cancellated; aperture rounded; peristome 
entire, continuous; outer lip slightly expanded and thickened ; 
operculum sub-spiral. 
The animal has long, slender tentacles, with eyes on small 
prominences near their outer bases; the foot is pointed behind; 
the operculigerous lobe has a wing-like process and a filament 
(cirrus) on each side. Lingual teeth single, sub-quadrate, 
hooked, dentated; uncini 3; 1 dentated, 2, 3, claw-shaped. 
They range from high-water to 100 fathoms, but abound most 
in shallow water, near shore, on beds of fucus and zostera. - 
Distribution, about 70 species. Universally distributed, but 
* It is much to be regretted that some modern naturalists have tried to find out and 
bring into use the obscure genera of Risso, and the worthless fabrications of Montfort 
and Rafinesque, which had better have remained unknown, 
