PLANORBIS. 45 



at the same time tar within its shell, which, as is the 

 case with the other members of the genus, is con- 

 siderably larger than the body of the animal. Moquin- 

 Tandon says that it lays its eggs during the months 

 of April, May, and June ; they vary in number from six 

 to twenty-one, are glossy, of a roundish form, and 

 enclosed in from eight to ten capsules which are 

 either roundish or oblong. It is rather difficult to 

 distinguish this from the last species, and some con- 

 chologists are consequently doubtful as to their being 

 specifically distinct ; but the shell of P. coviplanatiis 

 is rather larger and thicker than that of P. cari?iattis, 

 the whorls are more rounded, the keel is placed on 

 the lower side instead of near the middle of the 

 periphery, and the mouth is more roundly oval and 

 scarcely so angular above. Monstrosities occur in 

 this as in most of the species of Planorbis, having 

 their whorls more or less separated from each other. 



Var. I. rhombea. — Shell smaller, more solid, more convex 

 above, deeply umbilicated below ; keel blunt and almost 

 obsolete. Near Dublin and in the South of Ireland, B.C. Erith, 

 Kent (H. LesHe), J.C. 



Var. 2. albida. — Shell whitish or colourless. Eltham in 

 Kent (Choules), B.C. 



D. Whorls roiinded, not keeled. 

 10. P. cor'neus,* Linne. Pl. IV. 



Body shiny black or dark red above, greyish beneath ; 

 tentacles filiform, slender, rather opaque, of a dirty brown 

 colour, slightly rounded at the tips, diverging considerably at 

 their base ; eyes rather small, round, black ; foot opaque, 

 blackish, with reddish margins, covered with small, round, 



Horn-coloured. 



