224 NATURAL HISTORY. 



two retractile tentacles, bearing the eyes ; more than seventy rows of lingual teeth, 109 in a row, 

 i.e., a single symmetrical tooth in the centre, and fifty-four lateral teeth on each side. 



The Oncidia are found living on aquatic plants in marshes in the warmer parts of the world ; 

 others frequent sea-shores on rocks near the surface of the sea, ascending and descending as the tide 

 rises and falls. Sixteen species are found in Britain, the Red Sea, Mediterranean, etc. 



Genus Vaginulus. This animal is like Oncidium, but with four tentacles, the lower pair of which 

 is short and bifid. Vaginulus inhabits forests, living amongst decayed wood and under leaves. Six 

 species are known in the West Indies, India, South America, and the Philippines. 



FAMILY XXX.-LIMX.ELtLE. 



The Limnteidae, or Pond Snails, are widely distributed over the globe, and are plentiful in 

 individuals, but the species are few, and they are far less vaiiecl in the Old World than in the New. 

 We have almost as many species in Britain as exist in all Europe. 



Genus Limncea.* The shell is ovately turreted, thin, horny ; spire elongated and sharply pointed ; 

 body-whorl ventricose ; aperture large. The animal has a broad short head 

 and flattened tentacles ; eyes near the inner bases. The Limncece inhabit fresh 

 water, and feed chiefly on decaying leaves ; they deposit their spawn in oblong 

 transparent masses on water-plaftts and stones. They glide beneath the surface 

 of the water, shell downwards, and hibernate in the mud. Fifty species are 

 found living in Europe, Madeira, India, China, and North America. 



The genus Chilinia has a thin oval shell, marked with wavy bands or 

 dark spots ; columella plicated and thickened. Fourteen species occur in 

 South America in running water. 



The shell of Physa is a left-handed spiral ; the aperture is rounded 

 in front ; the mantle has an expanded margin, bordered with long filaments. 

 Twenty species occur in America, Europe, South Africa, India, and the 

 Philippines. 



Genus Anvylus, " River Limpet." The shell is Limpet-shaped and thin; 

 the apex left-handed. The animal is like Limncea. Fourteen 

 LIMNJEA STAGNALIS. species are found in running streams, attached to stones and aquatic 



plants in Europe, North and South America. 



Genus Gundlacftia. The Shell is thin, obliquely conic ; two-thirds of base closed by a 

 flat horizontal plate. It is found in fresh water in Cuba. PHY -AC 



Genus Planorbis. The shell in Planorbis is discoidal : the apex is sunk in the nucleus of TAXEA. 

 the coil; whorls three to seven in number, smooth or striated; sometimes keeled along the 

 border. The body is slender, the head obtuse ; tentacles long and bristle-like, with the eyes at their 

 bases ; foot small and narrow. " Planorbis inhabits all kinds of stagnant pools and ditches and gently 

 lunning brooks, chiefly adhering to flags and other water-plants. When left dry in the bed of a 

 stream by retiring water, the animal encloses itself within the shell by an epiphragm." (Reeve.) 

 Sixty species occur in Europe, North America, India, and China. It is common in England. 



FAMILY XXXL AURICULIDJE. 



The Auriculidai were long regarded as marine shells ; they frequent salt marshes, clamp hollows, 

 and places overflowed by the sea. They have a spiral shell coated with a horny epidermis ; the body- 

 whorl is large, the spire very short ; the aperture ear-shaped ; the columella plaited. The animal 

 absorbs the internal column of its shell. It has a broad short head with two tentacles, the eyes 

 behind them ; orifices as in Snails. 



Genus Auricula.-^ The shell has an obtuse spire, covered with a dark epidermis ; outer lip 

 expanded and thickened. Fifty species are found living within the tropics, the Philippines, Celebes, 

 and Peru. 



Genus Carychium. This small mollusc has an oblong, finely striated shell ; the aperture oval 

 and toothed. It has two blunt cylindrical tentacles; the eyes are black and near their bases. 

 One species, from the caverns of Carniola, is blind. 



* Limnuios, Greek, marshy. t Latin, auricula, little ear.. 



