PLANORBIS. 237 



Var. 1., shell smaller, -with the transverse laminae more re- 

 mote : Planorbis cristatus. Drap. Hist. p. 44. t. 2. f. 1 — 3. 



Var. 2., with the transverse laminae obliterated. 



Monstrosity, with the volutions detached and raised above 

 each othei'. 



In ponds and ditches, on aquatic plants. 



Animal grey. 



Shell the tenth of an inch in diameter, of a black- 

 ish or greenish horn-colour, with three volutions; 

 the epidermis raised into numerous transverse ridges, 

 which form a spinous crest round the outer margin ; 

 aperture roundish-oval, united all round, and often 

 detached from the second volution at its narrower 

 end. 



M. de Quatrefages observes that, if a young Pla- 

 norbis imhricatus is examined with a weak magni- 

 fying power, red blood is to be seen to fill the cavity 

 of the pericardium and the ventricle, and at moments 

 to colour the general cavity of the whole body on its 

 lower surface ; he has not seen any distinct globules 

 in this blood ; other specimens of a very small size 

 have colourless blood. {Ann. and Mag. N. H. xvii. 

 454, 1844.) 



c. Spire flat; ivhorls Jlat above, keeled. (Gyrorbis.) 



107. 5. Planorbis carinatus. Carinated Coil Shell. 

 — Shell horn-colour, transparent, striate, near- 

 ly flat above, rather convex and with a slight 

 central umbilicus beneath ; whorls six, rapidly 

 enlarging, with a prominent obtuse keel in the 

 middle; mouth angular, (t. 8. f. 89.) 



Planorbis carinatus. Bliiller, Verm, ii, 157.; Drap. p. 46. t. 2. 

 f. 13, 14. 16.; Brard, p. 150. t. 6. f. 3. ; Turto7i, Man. ed. 1. 



