The Shell-Collector’s Handbook. 67 
v. compressa (Lloyd) : Shell more concave below than 
in the type, and only depressed in the centre on the 
upper side; the whorls also are rounder, and do not in- 
crease so quickly, making the whole shell more compact. 
PLANORBIS SPIRORBIS, MULLER. 
SHELL concave above, flat below, or the reverse, thick, 
horn-coloured ; whorls five to six, rounder, and with the 
keel not so well pronounced as in P. albus, the body-whorl 
not exceeding jth the length of the spire; mouth 
roundish ; peristome often white-ribbed ; umbilicus wide, 
but shallow. Animal grey, tinged with purple or red. 
Hatitat.—Shallow and stagnant water, sluggish streams. 
v. ecarinata (Jeff.): Shell smaller, light grey, having 
one whorl less than usual, and no trace of a keel. B. C. 
vol. i.,p. 87. (=P. spirorbis, Mog. Tand, Moll. Fr., p. - 
437, pl. xxxi., f. 1-5.) 
v. albida (Nelson): Shell white. 
m. scalariforme: Shell reversed. 
PLANORBIS VORTEX, LINN. 
SHELL concave above, flat below, extremely depressed, thin, 
pellucid, glossy, brownish horn-colour, marked with fine 
and regularly disposed strize in line of growth; whorls six 
to eight, gradually increasing in size; the outer whorl 
rounded so as to form a sharp keel on its lower margin; 
mouth rhombic, compressed ; umbilicus large and shallow. 
Diameter of shell 2 of an inch. Animal violet-brown. 
Habitat.—Shallow and stagnant waters. 
v. compressa (Mich): Shell thinner, flatter; keel 
more distinct, sharper, and placed nearly in middle of 
periphery. (=P. compressus, Mich., Compl. p. 81., pl. xvi., 
figs. 6-8). 
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