BULLETIN OF THE LABORATORIES 
84 
V entral valve convex, with a broad, undefined depression extending 
from near the centre to the anterior margin ; beak a little incurved, 
cardinal area directed backwards, incurved. Owing to the depression 
along the anterior portion of the ventral valve, the shell has a sinuous 
outline in front. 
Surface marked by fine, close, branching striae, which are arched 
upwards along the postero-lateral margins ; radiating striae crossed by 
several lines of growth. Concentric striae not distinguishable in the 
specimens at hand. 
Length, 17 mm.; breadth, 19 mm.; convexity, 8 mm.; hinge line, 
10 mm. 
Locality and positmi. Soldiers’ Home Quarry, in the upper, shaly 
courses of the Clinton Group. 
VIII. Orthis elegantula, Dalman. 
{Plate XII Figs, ii a, h.) 
Shell semi-oval ; hinge line shorter than the width of the shell, 
exceeding the length of the cardinal area. 
Dorsal valve almost flat, with a shallow depression extending from 
the beak to the anterior margin ; more marked near the beak ; beak 
not incurved. 
Ventral valve convex, extremely elevated towards the beak; beak 
much exceeding that of ventral valve in length, and incurved over 
the cardinal area. 
Surface marked by fine radiating striae, branching, curved upwards 
along the lateral and posterior margins ; crossed by lines of growth, and 
fainter concentric striae. 
This species may be readily distinguished from O. hyhrida by the 
flat dorsal valve, and shallow depression extending from the beak to 
the anterior margin, also by the more quadrangular outline of the 
shell. 
Length, 16 mm.; breadth, 17 mm.; convexity, 4 mm.;' hinge line, 
10 mm. 
Locality and position. Soldiers’ Home and Centreville Quarries, 
in the upper courses of the Clinton Group. 
