GASTEEOPODA. 266 



Sliells extremely like the recent pJiorus, are met with even in 

 the carb. limestone and lias. 



Lacuna, Tui-ton. 



Etymology, lacuna, a fissure. 



Type, L. paUidula (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 cusj^ed ; uncini 1, 2, dentated, 

 3 simple. Spawn [ootlieca) yermiform, thick, semi- circular. 

 Eange, low water — 50 fathoms. 



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

 Sj)ain. 



Fossil, 1 species. Glacial beds, Scotland. 



LiTioPA, Eang. 



Etymology, litos, simple, ope, aperture. 



Type, L. bombyx (PI. IX., Fig. 24). 



Shell minute, jDointed ; aperture slightly notched in front ; 

 outer lip simple, thin ; inner lip reflected ; ojperculum spiral. 



Distribution, 6 species. Atlantic and Mediterranean, on float- 

 ing sea-weed, to which they adhere by threads. 



Fossil, 1 species. Pliocene (Crag). 



EissoA, FremenTiUe. 



Etymology, named after Eisso,* a French zoologist. 



Type, E. labiosa (PI. IX., Fig. lY). 



Synonym, Cingula, Flem. 



(S/ie?^ minute, white or homy; 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, dentatod; 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 tliat some modem naturalists have tried to find out and 

 bring into use the obscure genera of Kisso, and the wortliless fabrications of Montfort 

 and Kafinesque, which had better have remained imknown. 



