LAMELLIBRANCHIA TA. 
313 
Test thin, marked by moderately strong concentric striae, which are raised 
into varices or concentric undulations at irregular intervals. 
Anterior muscular impression just within the anterior border, above the 
longitudinal center of the shell. 
The three specimens figured measure respectively 45, 37 and 34 mm. in 
length, and 35, 28 and 27 mm. in height. 
This species differs from any other described, in the stronger curvature of the 
basal margin, bringing the termination of the umbonal ridge higher, and giving 
a proportionally narrower cardinal slope and posterior end; in other respects, 
it is very similar to the M. tmuistriatus of the Hamilton group. 
Formation and locality. In the Waverly sandstones of Licking county, 0. 
NUCULA, Lamarck. 1799. 
Nucula niotica. 
PLATE XLV, FIGS. 1, 2. 
Nucula niotica, Hall and Whitfield. Twenty-fourth Ann. Rep. N. Y. State Mus. Nat. Hist., p. 190. 1872. 
“ “ “ “ Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 45, 
figs. 1, 2. 1883. 
Shell small, obtusely sub-cuneiform; length a little greater than the height; 
basal margin regularly curving, rounded posteriorly; cardinal margin very 
oblique ; anterior margin vertically truncate. 
Yalves very gibbous. 
Beaks anterior, incurved. Umbo prominent. Umbonal slope very gibbous. 
Test thick in the upper part, marked by fine, even, concentric striae, which 
are aggregated into fascicles of growth. 
The internal casts show strong anterior and posterior muscular impres¬ 
sions, and three distinct umbonal muscles; there are seven or more pos¬ 
terior, and five anterior teeth in a specimen of medium size. 
An internal mould has a length of 17 mm., and a height of 13 mm. A 
specimen preserving the test has a length of 18 mm., and a height of 16 mm. 
