122 MONOGRAPH OP THE GENES STROPHIA. 
where the shell slopes abruptly to a blunt point, forming an angle of 
sixty-eight degrees. The striations are not numerous, twenty-three to 
the first whirl, are rather prominent, quite regular, but not arianged 
in lines, nearly straight on the first four whirls, but are slightly 
inclined from right to left on the lower whirls ; they are not furrowed 
but are smoothly rounded, and are about as wide as the interspaces 
Fig. 36. 
between them. 
Aperture, small and contracted at the entrance, measuring a little 
more within than at the margin. Lower tooth, quite prominent, about 
.04 high, less than twice as long as 
high; it is slightly elevated. The 
upper tooth is about as high as the 
lower, and extends backward around 
the column. 
Margin, not produced forward as 
far as the diameter of the shell, is 
slightly inclined to the right, but not 
beyond the diameter of the shell, but 
the upper whirl bulges out from it on 
the left, about half the width of the 
aperture. The margin is not thick- 
ened, and the only lateral projection 
from it is on the left, and that is 
slight. The frontal bar is thin, but interrupts the striations. 
Color of shell, externally, ashy brown, with the striations creamy 
white. Internally, dark-brown, creamy white on edge of margin and 
on teeth. 
Nigjf 
B 
I 
Strophia cinerea robusta. 
B, - ide view, of type. 
A, front view, 
DIMENSIONS. 
Size of type, 1.12 by .55. Largest specimen, 1.37 by .50; small- 
est, .97 by .30. Greatest diameter, .55 ; smallest, 30. Largest 
specimen, 1.25 ; shortest, .97. 
OBSERVATIONS. 
Individual variation is considerable, but is mainly toward a 
cylindrical form with a thickened margin through which this sub- 
species intergrades with typical S. cinerea. hut thiough a small 
percentage of specimens, some of which have ten whirls. The 
margin of some specimens is also thickened. A decided form is as 
follows : 
