173 MANUAL OF THE MOLLUSCA. 



■ TDpe, A. fluviatilis. Mull. PL XII. fig. 33 (Patella lacustris, L.) 



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

 a sub-spii-al muscular scar. 



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

 gual teeth 37.1.37, in 120 rows, centrals small, laterals \Tith 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) SheU 

 and animal dextral; lingual teeth 40, in 73 rows. 3 sp. West Indies, 

 Em-ope. Fossil, 2 sp. Eocene. Brit. France. 



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

 plate, tm-ned up and notched on one side. N. Zealand. 



Planorbis, MiiUer, 



Si/n. " Coret," Adans. T//pe, P. corneus, PI. XII. tig. 34. 



S/iell 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-quadi-ate, central and marginal bi- 

 cuspid, laterals tricuspid ; excretoiy orffices on left side of the neck. 



Some species of Flanorbis have the sutures and spire deeply 

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

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

 6,000 teeth, {Cocken). P. corneus secretes a purple fluid 

 (Lister). P. lacushis (Segmentina,' Fleming) has the whii'ls 

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

 radiate openings. 



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



Fossil, 60 sp. Wealdeik — . Brit. France. 



FAMILY V. AuRicuLiD^. 



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

 apertm-e elongated, denticulated ; internal septmn progressively absorbed. 



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

 sessile behind them; mantle-mai'gin 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 3 1 laterals 

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

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

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



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



