82 VICTORIA MEMORIAL MUSEUM. BULLETIN NO. I 
thisina cava, Barrande, and probably Tripleaia grayics , Davidson, 
though the interior of the latter is not known. 
OXOPLECIA CALHGUNI Sp. nOV. 
Shell transversely oval, biconvex, with sub-rectangular fold 
and sinus. The greatest width is about the middle of the 
shell. The brachial valve is much more gibbous than the 
pedicle and has a well-defined fold, somewhat fiat on top, be- 
ginning close to the beak and rising gradually until at the 
anterior margin its sides are abrupt. Both valves are covered 
with radiating plications, averaging about 5 in 3 mm., near the 
front, though coarser and finer ones are arranged in somewhat 
irregular groups on the side lobes. Adult specimens have 7 
plications in the sinus, and of the 8 on the fold the two marginal 
plications are much stronger. Concentric growth lines cross the 
plications of both valves. The width at the hinge line is a 
little more than half the width of the shell, and the cardinal 
angles are very obtuse. The beak of the brachial valve is 
incurved but prominent, and there is no cardinal area on this 
valve. A faint ridge extends along the umbonal region of a cast 
of the pedicle valve to the end of the beak, which is very long 
and definitely incurved. The cardinal area of this valve is 
triangular, and slightly concave, owing to the curve of the beak. 
The delthyrium is covered by a flat deltidium which occupies 
a little less than a third of the whole area. The interior of the 
pedicle valve shows two dental supports between which projects 
the bifid cardinal process of the brachial valve. 
Length of the largest specimen about 16 mm., width 21 mm., 
height 12 mm. 
Oxoplecia calhouni is most nearly allied to Tripleaia ulrichi, 1 
Winchell and Schuchert, of the Maquoketa of Minnesota, but 
differs from it in that the fold and sinus are more prominent 
in the former, and begin nearer the beak; the top of the fold is 
flatter, and the abrupt sides of both fold and sinus are without 
plications; the two marginal plications of the fold are also very 
marked in Oxoplecia calhouni. In this species too, the con- 
centric growth lines are more prominent, and the brachial valve 
is much more convex than in the Minnesota species. 
’■Minnesota Geol. Sur. Ill, 1893, p. 409, fig. 34. 
