MONOGRAPH OF THE GENUS STROPHIA. 
its length from the frontal bar. The upper tooth is also a mere tuber- 
cle, is placed at least as far back as in the lower, but extends back 
around the column. 
The margin is produced forward about as far as the diameter of 
the shell, is a little inclined backward, and slightly to the right, beyond 
the diameter of the shell; it is very thin, a little rolled over, with the 
edge sharpened. The frontal bar is very slightly developed, merely ex- 
tending from one striation to the other, thus filling in the interspaces 
but not crossing the striations. The striations appear within it, even 
more prominently than on the outside, and they occur on the septa 
throughout the entire length of the interior of the shell. 
Color of shell, externally, bluish white, marked with rather longi- 
tudinal patches of pale reddish brown which are irregularly distributed 
over the surface of the shell, and which are scarcely more abundant on 
the lower whirls than on the upper. 
DIMENSIONS. 
Size of typical specimen, .75 by .32. Largest specimen, .76 by .35. 
Longest specimen, .77 ; shortest, .63. Largest diameter, .32 ; smallest, 
.25. 
OBSERVATIONS. 
Individual variation consists in more or less markings, but these 
are never so numerous as to form the predominating color of the shell as 
in S. cyclostoma. One of the chief external characters of this shell is 
the sharply defined striations which rise abruptly from the shell. In 
S. cyclostoma these rise gradually from the shell at a considerable an- 
gle and are finer. The teeth are set further back in S. microstoma and 
are less prominent. Another noticeable internal feature in this species 
is the prominences of the striations, not only at the mouth, but also on 
the septa quite to the lower whirls. 
There are four well defined forms as given below. 
Form No. 1. Pure white in color, without fleckings. The mouth 
is rather more contracted and the striations are less prominent, other- 
wise similar to the type. 
Form No. 2. White in color, unflecked, but larger (.75) and 
more cylindrical, the first four whirls being about equal in size. Whirls 
10 . 
Form No. 3. Colored as in the type, but much more slender pro- 
portionately, and much smaller, size, .62 by 25. 
Form No. 4. Very small, but otherwise a miniature of the type, 
size, .57 by .27. 
