MONOGRAPH OF THE GENUS STROPHIA. 
139 
Margin produced forward beyond the diameter of the shell, 
is inclined to the right beyond the diameter of the shell ; is 
thinner than the shell behind it, and the edge is sharpened without 
being rolled over, but is much roughened on the sides by lines of 
growth. The frontal bar is developed to a remarkable degree, pro- 
truding far beyond the shell (.03), as far, in fact, as the rest of the 
margin, and has three or four lines of growth between its edge (which 
is thin, sharpened as in the other portions of the margin) and the 
striations. 
Color of shell, throughout, externally, dull white; internally, deep 
brown, fading into white on the tooth and margin beyond it. 
DIMENSIONS. 
Size of type, 1.25 by .55. Largest specimen, 1.40 by .07 ; 
smallest, 1.05 by .47. Longest specimen, 1.40 ; shortest, 1.05. 
Greatest diameter, .67 ; smallest, .47. 
OBSERVATIONS. 
Individual variation is mainly in the direction of a form with 
fewer striations, sometimes as few as thirteen only are found. Some 
individuals have the upper tooth developed, then there are more 
striations, and the margin is thicker, with the edge smoothed and not 
sharpened as in the type. I regard these specimens as decided rever- 
sions toward S.. ritchiei which is undoubtedly the parent stock of this 
species. In concluding that S. ritchiei is the older species I have 
been guided not only by the fact that S. grayi shows considerable 
reversion towards that species, but also because S. grayi appears 
quite unsettled, for it has not only produced three well marked forms, 
but two other forms which I must regard as sub-species. The three 
forms are as follows : 
No. 1, shorter and proportionately thicker than in the type (1.10 
by .57) ; whirls, ten, the first three of which are about equal in 
diameter. Margin not produced forward as far as the diameter of the 
shell, and with the edges slightly rounded. Striations, twenty to the 
first whirl. Tooth and color, as in the type, but the upper tooth is 
present, but small. Variations are toward producing a sub-form 
with a thickened margin, bnt in some cases the margin is produced 
forward with the edge upward. These are about one per cent, of this 
form. 
