PLANORBIS. 243 



though he was not perhaps aware of the manner in 

 which it was formed. 



110. 8. Planorbis spirorhis. Rolled Coil Shell. — 



Shell thin, brown, slightly concave on both 



sides, with six gradually increasing roundish 



and nearly equal volutions ; mouth roundish. 



(t. 8. f. 98.) 



Helix spirorbis. Linn. S. N. 1244. ; Mont. T. B. p, 455. t. 25. 

 f. 2. — Planorbis spirorbis. Aliiller, Verm.n. 161.; Brai'd, 

 p. 156. ; Brap. H. M. ii. t. 2. f. 8, 9. ; Turtoii, Man. ed. 1, 

 115. f. 98.; Sturm, Fuunn, t. 45.; Leach, Syn. Moll. 112.; 

 Forbes and Hanley, B. M. iv. 159. t. 127. f. 9, 10. 



In ponds and canals. 



Shell in flatness and compactness of volutions 

 much resembling the P. vortex, but is less and has 

 only six volutions, and is rather thicker ; the upper 

 surface is a little concave, in consequence of the 

 volutions being rounded, and the outer one scarcely 

 flattened into a carinated edge ; and the aperture is 

 rounded below. 



Mr. Alder now believes that P. vortex and P. 

 spirorhis of Mliller are distinct. (See Alder, Cat. 

 ISupp. 2.) 



The peristome is often white-ribbed. 



d. Shell polished ; spire deeply umhilicate ; whorls 

 slightly keeled ; front of shell convex. (Hippeutis.) 



111. 9. Planorbis /y^ii'anew. Fountain Coil Shell. 



— Shell depressed, dark horn-colour, smooth, 

 glossy, diaphanous, flat above, with a central 

 sunk spire, rather convex beneath; whorls 

 three or four, the outer shelving to a keel in the 

 middle; mouth elongate-angular, (t. 8. f. 93.) 



K 2 



