PLANORBIS. 161 



Shell small, brownish horn-colour, about thrice as broad 

 as high, not much polished. Upper or right disk flattish, 

 yet slightly concave in the middle, exhibiting six ex- 

 tremely narrow coils, that are of very slow increase, closely 

 and most minutely wrinkled across, deeply divided by the 

 suture, rounded, but with their inner slope the more abrupt. 

 Lower disk very deeply and broadly excavated in the 

 middle ; the body-whorl about twice as broad as on the 

 other disk, and slightly more slanting from its rounded 

 periphery. Mouth unarmed, peculiarly small, occupying 

 only about a sixth or seventh of the total breadth, of a 

 narrow lunate figure, not peaked, a little below the level 

 above, slightly beyond it beneath. Outer lip neither 

 dilated, marginated, nor strictured behind. Size, a fifth 

 of an inch, by about a line in height. 



Animal dark grey, nearly black, very small in propor- 

 tion to the shell. 



Generally distributed through the British Islands, in- 

 habiting ponds, ditches, and slow streams. 



P. NiTiDus, Midler. 



Polished smooth, transparent, devoid of septa ; body dispro- 

 portionately large, angulated at the periphery. 



Plate CXXVII. fig. 11, 12. 



Planorhis mtidus,MvLLER,Yerm. Hist. vol. ii. p. 163, in part. — Flem. Brit. 

 Animals, p. '278. — Jeffreys, Trans. Linn. Soc. vol. xvi. 

 p. 388, 522. — Alder, Trans. Nat. His. Soc. Northumb. 

 vol. i. p. 30. — Gray, Manual L. and F. W. Shells, p. 268, 

 pi. 8, f. 93. — Thomps. Ann. Nat. Hist. vol. vi. p. 125. — 

 Brown, 111. Conch. G. B. p. 33, pi. 14, f. 50, 51. — Lam. 

 Anim. s. Vert. (ed. Desh.) vol. viii. p. 388 (not synonyms). 



Heliic foniuna , Lightfoot, Phil. Trans. 1786, vol. ixxvi. p. 165, pi. 2, upper 

 compartment. — Mont. Test. Brit. vol. ii. p. 462, pi. 6, f. 6.— 

 Maton and Rack. Trans. Linn. Soc. vol. viii. p. 193. — Rack. 



VOL. IV. Y 



