172 MANUAL OF THE MOLLUSCA. 



Type, A. fiuviatilis, Mull. PI. XII. fig. 33 (Patella lacustris, L.) 



Shell conical, limpet-shaped, thin ; apex posterior, sinistral ; interior with 

 a sub-spiral muscular scar. 



Animal like Limnsea ; tentacles triangular, with eyes at their bases ; lin- 

 gual teeth 37.1.37, in 120 rows, centrals small, laterals with long recurved 

 hooks. 



Distr. 14 sp. N. and S. America, Europe, Madeira. On stones and 

 aquatic plants in running streams. Fossil, 8 sp. Eocene, Belgium. 



Sub-genera, Velletia (oblonga, Lightf.) Gray. (Acroloxus, Beck) Shell 

 and animal dextral; lingual teeth 40, in 75 rows. 3 sp. West Indies, 

 Europe. Fossil, 2 sp. Eocene. Brit. France. 



Latia (neritoides) Gray; shell limpet-like, interior with a transverse 

 plate, turned up and notched on one side. N. Zealand. 



PLANORBIS, Miiller. 



Syn. " Coret," Adans. Type, P. corneus, PL XII. fig. 34. 



Shell discoidal, dextral, many- whirled ; aperture crescentic, peristome 

 thin, incomplete, upper margin projecting. 



Animal with, a short, round foot ; head short, tentacles slender, the eyes 

 at their inner bases ; lingual teeth sub-quadrate, central and marginal bi- 

 cuspid, laterals tricuspid ; excretory orifices on left side of the neck. 



Some species of Planorbis have the sutures and spire deeply 

 sunk, and the umbilicus flattened ; specimens occur with the spire 

 elevated (fig. 97*). P. contortus, a minute species, has above 

 6,000 teeth, (Cocken}. P. corneus secretes a purple fluid j 

 (Lister). P. lacustris (Segmentina, Fleming) has the whirls 

 contracted, internally, by periodic septa, 3 in a whirl, with tri- 

 radiate openings. 



Distr. 60 sp. N. America, Europe, India, China. 



Fossil, 60 sp. Wealder . Brit. France. 



FAMILY V. AURICULID^E. 



Shell spiral, covered with horny epidermis, spire short, body-whirl large ; 

 aperture elongated, denticulated ; internal septum progressively absorbed. 



Animal with a broad and short muzzle, tentacles 2, cylindrical, the eyes 

 sessile behind them; mantle-margin thickened; orifices as in the snails; foot 

 oblong ; sexes united ; mouth with a horny upper jaw ; lingual teeth numer- 

 ous, central series distinct, hooked, tricuspid. A. livida has about 31 laterals 

 (Loven) ; another species examined by Mr. Wilton has 11 large laterals and 

 about 100 smaller (uncini) on each side, gradually diminishing towards the 

 edge, fig. 98, c. central teeth, /. laterals. 



* P. marginatus, var. Rochdale, communicated by J. S. Gaskoin, Esq. 



