MONOGRAPH OF THE GENUS STROPHIA. 
165 
DESCRIPTION. 
R 
Sp. Ch. Size, medium. Shell, of medium thickness. Striations, 
present. Whirls, ten. Examined 2,000 specimens. 
Form of shell, a pointed cylinder, the first, second and third 
whirls being about equal in diameter, then the shell slopes gradually 
to a rather blunt point, forming an angle of seventy degrees. The 
striations are not very numerous, twenty-three to the first whirl ; 
they are rather regular, narrow, not quite as wide as the interspaces, 
are inclined to be triangular, 
but are slightly rounded, Fig. 53 . 
smooth, but somewhat furrowed, 
are only partly arranged in 
lines and a little inclined from 
right to left. 
Aperture, quite small, in- 
clined to be rounded, open at 
the entrance, but contracted 
within. Lower tooth, promi- 
nent, double, with the second 
smaller and placed on the left 
of the larger ; the larger tooth is 
about .05 high, about as wide 
as high and not twice as long 
as high, the smaller one beside 
it is about half as large and is 
closely connected with the larger ; both are somewhat elevated, are 
about central in position, and are placed back a little less than once 
the length of the larger from the central bar. The upper tooth is a 
mere tubercle, is elevated a little above the top of the lower tooth and 
the space between the two is inclined to be filled up. 
Margin produced forward about as far as the diameter of the 
shell, it is thin, about as thick as the shell behind it, and is smoothly 
rounded, without being produced into any edge. Immediately behind 
this first margin is a second margin with the edge roughened and 
between this double margin the shell shows lines of growth, having, in 
fact, formed the inner margin first, then, after adding more to the shell, 
formed a new margin. The frontal bar is well developed and com- 
pletely interrupts the striations. 
Color of shell, externally, pure white, rather lustrous, internally 
B 
C 
Strophia bimarginata. A, front view; B, side 
view of type. C, young, enlarged, D, margin 
of another adult specimen. 
