MONOGRAPH OF 'THE GENUS STROPHIA. 
169 
equal in diameter, then the shell slopes to a moderately acute point, 
forming an angle of sixty-two degrees. The striations are not 
numerous, twenty to the first whirl, they are narrower than the inter- 
spaces between them, regular, and somewhat broken, but smoothed on 
top, not arranged in lines, and are slightly inclined from right to 
left. The spaces between them are narrow, with one or two distinct 
lines or ridges of growth. 
Aperture, rather small, arched, but open, and inclined to be 
rounded. Lower tooth, prominent, inclined to be double, about .03 
high, wider than high, and about twice 
as long as wide, is slightly elevated, 
and placed in a central position and 
back not quite once its length from the 
frontal bar. The upper tooth is repre- 
sented by a mere tubercle. 
Margin, not produced forward 
quite as far as the diameter of the 
shell, is about twice as thick as the 
shell behind it and is smoothly 
rounded, with the sides slightly 
furrowed with lines of growth. The 
frontal bar is quite well developed and strophva bjmarginala cera - A « front - ® 
. margin, of type. 
protrudes a little beyond the striations. 
Color of shell, externally and 
internally, is a beautiful waxy white, without tinting or marking of 
any kind. 
DIMENSIONS. 
Size of type, 1.00 by .40. Largest specimen, 1.07 by .47 
smallest, .97 by .45. Greatest diameter, .47 ; smallest, .40. Longest 
specimen, 1.07 ; shortest, .97. 
OBSERVATIONS. 
Individual variation, on one hand, is toward the parent stock, S. 
marginata, the margin being: wide, but never double, and the 
interior slightly tinted with very pale browm, and on the other hand, 
toward specimens with a thinner margin, showing no lines of growth, 
and a single small tooth as beautifully white in color as in the type. 
There is a singular resemblance between this sub-species and 
