232 
white, rather glossy, opaque, faintly and longitudinally 
rugose whorls, outer margins thin but no carinate ; all 
the turns apparent on both sides, the last very large ; 
mouth large, obovate-oblong, with a slightly thickened 
and somewhat spreading margin and a medial erect 
tooth extending to two thirds its height and enlarged 
and emarginated at the end. 0,08. Aberdeen. 
SPIROLOCULINA.—Macei1uivray. 
Suborbicular, depressed, with the cells curved and op- 
posed to each other in a siugle plane, and completely 
exposed or not embracing each other ; the aperture 
roundish at one end of the last turn. 
S. Concentrica. Macg. Aberd. p. 36.—Mtt1io1a. 
C. Brown Ill. t. 1. f. 22. Elliptic-orbicular, concave 
on both sides, very thin, of about five opposite arcuated 
cells distinctly separated by a groove ; outer cells exter- 
nally flattened or slightly convex ; white generally with 
two brown or blackish streaks on each turn; aperture 
nearly square with an erect tooth-iike process and thick 
brown margin. 0,04. Aberdeen. 
ARETHUSA. Moytrort. 
Cells arranged obliquely and alternately along an axis, 
with the mouths of all the chambers having an aspect 
