GASTJEHOfODA. 256 



Shells extremely like the recent phorus, are met with, even in 

 the carb. limestone and Has. 



Lacusta, Turton. 



Etymology, lacuna, a fissure. 



Ti/pe, L. pallidula (PL IX., 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) vermiform, thick, semi- circular. 

 Eange, low water — 50 fathoms. 



Distribution, 16 species. Northern shores, Norway, Britain, 

 Spain. 



Fossil, 1 species. Glacial beds, Scotland. 



LiTioPA, Eang. 



Etymology, litos, simple, ope, aperture. 



Type, L. bombyx (PI. IX., Pig. 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). 



EissoA, Premenville. 



Etymology, named after Eisso,* a Prench zoologist. 



Type, E. labiosa (PL IX., Pig. 17). 



Synonym, Cingula, Plem. 



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 eide. Lingual teeth single, sub-quadrate, 

 hcoked, 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 oifucus and zostera. 



Distribution, about 70 species. Universally distributed, but 



* It is much to be regretted that some moclem naturalists have tried to find out and 

 bring nt : us- the obscure genera of Kisso, and the worthless fabrications of Montfort 

 and Eafinesque, which had better have remained unknown. 



