Strophomena and Other Fossils 
83 
Specimens of this type are common in the middle or Clarks- 
ville division of the Waynesville bed, but they occur also in the 
upper or Blanchester division. Not infrequently they are wrin- 
kled obliquely along the hinge-line. As a rule, the radiating sur- 
face striae alternate moderately in size or are approximately 
equal. 
The vertical and geographical range of the variety of Stropho- 
mena planumbona which was described by James as Strophomena 
elongata is very imperfectly known. No attempt has been made 
so far to determine whether it has any value as a diagnostic 
fossil, characteristic of some definite horizon. 
In Stony Hollow, northwest of Clarksville, in Clinton county, 
Ohio, Strophomena elongata makes its appearance 1 foot above 
the base of the Clarksville division of the Waynesville member, 
or 1 foot above the top of the 5-foot clay section in which Ortho- 
ceras fosteri is common. From this horizon, Strophomena elon- 
gata ranges throughout the Clarksville division, occurring as far 
up as the lowest layers belonging to the lower Hehertella insculpta 
horizon. Throughout this Clarksville division, the radiating 
striations usually are subequal in size, or alternately larger and 
smaller. Specimens in which 3 finer striae occur between each 
pair of stronger striations are found, but are not common and 
are not characteristic of this variety. 
No species of Strophomena is found in the lower half of the 
Blanchester division of the Waynesville member, between the 
lower Hehertella insculpta horizon and the lowest horizon at 
which Strophomena nutans and Strophomena neglecta make their 
appearance. This is an interval of 12 feet. 
The more quadrate forms of Strophomena planumbona, which 
are present also throughout the Clarksville division, reappear 
at the lowest horizon containing Strophomena nutans and Stro- 
phomena neglecta, and continue to the top of the Waynesville 
member, and beyond the middle of the Liberty. The variety 
known as Strophomena elongata, however, appears to be repre- 
sented only by a few, not very typical, specimens near the base 
of the upper Hehertella insculpta horizon, in the upper part of 
the Blanchester division of the Waynesville. 
Along the Stony Brook, 1 mile southeast of Fort Ancient, in 
Warren county, Ohio, typical Strophomena elongata also occurs 
in the Clarksville division, making its first appearance 2 feet 
