Silurian Fossils 
71 
extending toward the inner surface of the brachial valve, but in 
no case has it been possible to demonstrate that these plates reach 
the brachial valve and form a spondylium. 
Shell apparently very thin except at the beak. Exterior marked 
by low, broad, and often rather indistinct radiating plications, 
which bifurcate in an irregular manner. In some specimens the 
median part of the pedicel valve is separated from the lateral parts 
of the shell by very slight depressions, while the median part of the 
brachial valve rises almost imperceptibly above the general con- 
vexity of the shell. Near the beak, the radiating plications are 
usually very indistinct. 
Form oblong. Length of one specimen, 35 mm.; width, 28 mm.; 
thickness, 16 mm. 
This species does not fit well into any of the divisions established 
for the pentameroids. It may be an ancestral form m which the 
spondylia are not yet strongly developed. Its affinities can not be 
determined more closely until the interior is better known. It is 
too flat for a Pentamerella. The absence of a straight hinge 
margin is characteristic. The term Platymerella is suggested. 
Clinton bed: at foot of cliff north of railroad bridge northwest 
of Riverside, two miles north of Mannie, Tenn.; Cedar Point, one 
mile north of station at Iron City, at top of ferruginous bed, along 
the railroad to Pinckney, Tennessee. 
? Stricklandinia dichotoma. 
{Plate I, Figs. 2 A, B.) 
Generic affinities uncertain, the interior being unknown; may 
be one of the Orthidce, but the surface ornamentation resembles 
that of Stricklandinia castellana. Hinge line straight, delthyrium 
open. Valve moderately convex, 23 mm. long, 30 mm. wide, pos- 
terior half of the shell marked by about 20 radiating plications, 
all of which, except those nearer the posterolateral angles, branch 
once dichotomously on the anterior half of the shell. Plications 
crossed by fine concentric striae which may escape attention if not 
well preserved. 
Clinton bed : at Riverside and Iron City, associated with Platy- 
merella manniensis ; also in the Clinton at the landing at Clifton, 
Tennessee. 
