PLATE XVm 
The known geographical distribution of Strophomena sulcata is indicated by 
the area included within the dotted line. The much more limited area covered 
by broken lines indicates the range of this species during Waynesville times. The 
lines directed diagonally upward and toward the left designate the area within 
which Strophoinena sulcata has been found at the lower Hebertella insculpta hori- 
zon, at the base of the Blanchester division of the Waynesville. The extension 
of this area by diagonal lines directed upward and toward the right indicates how 
much greater is the known geographical range of this species during the Clarks- 
ville division of the Waynesville. The remainder of the space included within the 
dotted line indicates how much farther the known range of this species extends 
in the Liberty and Whitewater beds. In place of using a single letter to designate 
the locality at which Strophomena sulcata is known, the letter is varied so as to 
designate the horizon instead, in accordance with the scheme indicated at the base 
of the plate. 
The distribution of Strophomena vetusta and of the various varieties of Stro- 
phomena planumbona is indicated by the letters V and P respectively. 
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