Notes on Cincinnatian Fossil Types 
309 
are moderately convex. From these lines, the surface slopes rather 
strongly toward the posterodateral angles, being more or less con- 
cave near the margin of this part of the shell. Along the median 
part of the brachial valve the shell is faintly elevated anteriorly, 
the elevation being separated from the antero-lateral parts of the 
valve by broad, shallow, almost obsolete depressions, also following 
directions radiating from the beak; these depressions are about 4 
millimeters apart at the anterior margin of the valve. There is a 
slight tendency toward a median elevation also on the pedicel 
valve, but this elevation has a width of scarcely 2 millimeters. The 
surface of the shell is marked by fine concentric lines, often 15 in a 
length of one millimeter. Fine radiating lines traverse the shell, 
especially along the moderately convex median parts, included be- 
tween the imaginary lines leading from the beak to the antero-lateral 
angles; within this space the radiating lines usually number about 
8 in a width of one millimeter. 
The interior of the brachial valve is characterized by a long 
median septum, extending nearly 11 millimeters forward from the 
beak, and attaining its greatest width and elevation within one milli- 
meter of the end, where its width is 1.2 mm., and its elevation 0.8 
mm. Two narrowly cuneate very shallow depressions extend 
forward for a distance of 7 mm. from the beak, one on each side of 
the septum, attaining a width of about 1.2 mm. at their anterior 
ends. At their anterior ends these cuneate depressions are limited 
quite distinctly by moderately elevated crescentic elevations ex- 
tending laterally from the median septum for a greater distance than 
the cuneate depressions themselves. The crescentic elevations and 
the narrowly cuneate depressions correspond to the central scars 
and the concrete laterals of Hall and Clarke, as figured by them in 
case of Lingula iowensis (Pal. New York, 8, pt. 1, 1892, pi. 1, fig. 
14). On each side of this pair of concrete laterals there is an ad- 
ditional very faint depression, similar to the pair figured by Hall 
and Clarke in case of Lingula iowensis, but much less distinctly 
defined. This pair extends forward from the beak a distance of 
about 5.5 mm., and also attains a width of slightly more than a 
millimeter, and is limited by a slight elevation anteriorly. Both 
pairs of shallow cuneate depressions apparently are due to the areas 
of attachment of muscles which enlarge and shift toward the front 
with advancing age. Of these areas of attachment there are four, 
the final location of which is indicated by the crescentic elevations 
