GASTEROPODA. 



101 



no neck lobes ; operculigerous lobes, with developed lateral 

 expansions, and in numerous species with a caudal fila- 

 ment; foot usually subangulated in front, acute behind, 

 in some species rounded at both ends ; lateral elements of 

 the tongue dissimilar, all with denticulated apices ; median 

 denticle and its flanking laterals very broad, and with 

 lobcd incurved apices.* — 80 species ; also fossil. 



The species of this genus are all small shells, and are 

 remarkably beautiful both in colour and form ; there are 

 28 species found on the sandy shores of Great Britain, 

 and others come from the Mediterranean, the seas of 

 Senegal, North America, and the West Indies. 



Jeffreysia. Alder. — Shell minute, transparent, co- 

 nical, aperture ovate, rounded below, lips 

 thin and united ; operculum horny, with a 

 curious projection. Animal, head elongated, 

 deeply cleft ; tentacula four, and flattish ; 

 the eyes very prominent, but far behind 

 the tentacula; foot two-lobed in front; the 

 tongue has a broad middle notched tooth, 

 and two lateral teeth on each side. — 2 a&S. 

 species. 



Found on sea-weeds, near low water, on the British 

 coasts ; the shells greatly resembling Rissoa, but the animal 

 differs principally in the eyes, which are constantly seen 

 through the transparent shell; also in the operculum, 

 which is semicircular, imbricated, with a strong rectan- 

 gular projecting plate from the straight side. 



Rissoina. UOrh. — Shell turreted, almost entirely 

 like llissoa, mostly ribbed longitudinally, the aperture 

 oval, having at the lower part a canal ; the operculum is 



* Forbes's British Moll. 

 H 3 



