231 
4:p.565. t. 15. f5.—F. p. 234.—Macg. Ab. p. 37. 
—Serpuia O. Walk. t.1.f. 4.—Turt. D. p. 155.— 
Oblong, oval, opaque, glossy white, somewhat com- 
pressed ; on one side a single longitudinal suture which 
seems to divide the shell into two parts; on the other 
side the middle compartment is surrounded by a faint 
depression, that separates it from the exterior one, and 
is more elevated; aperture a little produced, oval, the 
margin yellow. 0,04...Jn sand from Sulcomb Bay, 
Devon, rare. 
V. DisctrorME. Macg. Aberd. p. 319.  Orbi- 
cular, very thin, of four arcuated flattened turns, which 
are opaque, greyish or reddish white, moderately glossy, 
faintly rugose, striated longitudinally the outer margined 
with a bluish white keel ; on one side all the four turns 
apparent, on the other, three; aperture large, direct, 
oblong or even linear; margin parallel, rim _thickish 
and generally reddish brown, a medial erect tooth ex- 
tending to more than half the height of the mouth. 
0,08... Aberdeen. Differs from Intortum in its orbi- 
cularity, its lesser thickness, its thinner keel and 
much narrower mouth. 
V. Pranatum. Macg. Aberd. p. 319.—Roundish , 
very thin, of three arcuated, much compressed, yellowish 
