PLANORBIS. 1G3 



Moll. Auvergne, p. 65 (animal). — Cantr. Mem. Ac. Bruxel. 



vol. xiii. p. 167.— Gras, Mol. Terr, et Fluv. France, Appx. 



p. 18. — Stein, Schnecken Berlins, pi. 2, f. 21. 

 // lia nitida, Gmel. Syst. Nat. p. 3624 (from Miiller). 

 Natttilus lacustris, Lightfoot, Phil. Trans, vol. lxxvi. (1786,) p. 163, pi. 1. — 



Mont. Test. Brit. p. 191, pi. 6, f. 3. — Turt. Conch. 



Diction, p. 117. — Fleming, Edin. Encycl. vol. vii. pt. 1, 



p. 86. — Dillw. Recent Shells, vol. i. p. 339. — Wood, 



Index Testae, pi. 13, Naut. f. 3. 

 Segmentina lineala, Fleming, Brit. Animals, p. 279; Treatise Moll. Anim. (from 



Encycl. Brit.) pi. 7, f. 18. — Gray, Manual L. and F. W. 



Shells, p. 271, pi. 8, f. 99. — Brown, 111. Conch. G. B. 



p. 33, pi. 14, f. 48, 49. 

 Planorbis lineatus, Jeffreys, Trans. Linn. Soc. vol. xvi. p. 389. — Alder, Mag. 



Zool. and Bot. vol. ii. p. 114. 

 „ Nautikus, Kickx, Moll. Brabant, p. 66. 



„ clausulatus, Potiez and Mich. Gal. Douai, Moll. vol. i. p. 209. — 

 Walker, Test. Miimt. Rar. pi. 1, f. 28. 



Shell small, much depressed, highly polished, smooth, 

 transparent, of a reddish amber-colour, with a few (usually 

 three on the final coil) distant opaque white radiating 

 curved lines, which indicate the site of the internal septa 

 or partitions ; painted here and there, likewise, with a 

 brown line, the vestige of a previous stage of growth. 

 Upper disk convex, except just in the middle, where it is 

 indented, displaying four whorls, the first three of which 

 are very small, merely convex, and of moderately fast 

 increase ; lower disk flattened, somewhat broadly, pro- 

 foundly, and rather abruptly umbilicated. Body-whorl 

 extremely large, filling nearly the entire surface, very 

 much less high than broad, about equally wide above and 

 below, gradually and convexly shelving on the upper disk 

 to a sharply angulated sub-basal keel-like edge. Suture 

 fine. Mouth broader than high, filling about two-fifths of 

 the total width, unarmed, of a blunt arrow-headed shape, 

 being horizontally compressed and trigonally lunate. Outer 

 lip simple, acute, projecting a little below the basal level. 

 Diameter the fifth of an inch. 



