PLANOKBIS. 
243 
though he was not perhaps aware of the manner in 
which it was formed. 
110. 8. Planobbis 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. Muller Verm. ii. 161.; Brard., 
p. 156. ; I)rap. H. M. ii. t. 2. f. 8, 9. ; Turton, Man. ed. 1. 
115. f. 98.; Sturm., Fauna., 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. 
spirorbis of Muller are distinct. (See Alder ^ Cat, 
Bupp. 2.) 
The peristome is often white-ribbed. 
d. Shell polished; spire deeply umbilicate ; whorls 
slightly heeled ; front of shell convex, (Hippeutis.) 
111. 9. Planokbis fontanus. 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.) 
