NATURAL SCIENCES OF PHILADELPHIA. 
9 
rather large, very oblique, becoming distinctly arcuate upwards. Left valve 
very ventricose, with a tapering, incurved beak, closely approximated to its 
fellow ; body of valve regularly arched along the umbonal slope, from which 
line it describes a rapid convexity to the anterior margin, sloping more gradu¬ 
ally to the ventral margin and becoming gradually flattened toward the 
posterior ventral angle. The upper boundary of the body is an abrupt 
descent to the plane of the posterior wing, and sharply divides the two ; 
posterior wing sloping to the dorsal and posterior borders of the valve, 
produced above into a slender spine, nearly as long as the posterior end 
of the shell, with a deep sinuation below. Anterior ear short, saccate, less 
distinctly divided from the body of the valve. Hinge-line straight, with a long, 
posterior cartilage facet. Surface marked by irregular wrinkles of growth 
which become fine striae on the posterior wing, and sharp plications on the an¬ 
terior slope and auriculation. Right valve smoother and considerably less 
ventricose, with the posterior wing-surface divided from the body of the valve 
only by a slight groove. 
Length from beak to extremity of posterior wing -81 ; from beak to extremity 
of anterior wing -21; from middle of dorsal side to ventral side •10; greatest 
width of body of shell *48 ; same width in a larger specimen *93 ; depth of right 
valve of same specimen -30. 
An occasional specimen of this species, differing from the types of the above 
description only in the absence of arcuation of the body, presents a good agree¬ 
ment with Prof. Hall’s figure and brief diagnosis,—diverging only in the less 
forward direction of the beak, in the much larger anterior ear, and deeper 
byssal sinus beneath it. The prevailing forms greatly resemble Avicula lunu - 
lata , Phil. sp. (Geol. Yorks, ii. pi. vi. fig. 12). It is, however, less oblique, es¬ 
pecially in the earlier stages of its growth, and the beak is narrower and more 
depressed. It is also considerably broader on the antero-ventral side, and has 
a larger posterior wing. 
AYICULOPEOTEN, McCoy. 
Aviculopecten Caroli, n. sp.—Shell of medium size, subcircular, ventri¬ 
cose. Hinge-line shorter than the shell; anterior ear of right valve shorter 
than anterior end of shell, rounded, slightly inflated, with a deep, sharply- 
rounded notch below; posterior ear acute, slightly longer than the anterior, 
with a broad, shallow notch below; shell otherwise nearly equilateral. Beak 
central, inconspicuous ; greatest convexity of valve a little above the middle. 
External surface of the body of the valve marked by about 25 nearly equidis¬ 
tant, narrow, sharply-raised, radiating ribs, with two or three fine, raised striee 
in each of the interspaces; a set of very fine, sharp, close, concentric raised 
lines cross the smaller ribs, but are intercepted by the primary ones. The 
latter, however, show a tendency, toward the pallia! margin of the valve, to de- 
velope nodes, which, on the anterior and posterior slopes, become distinct spines. 
The spines sometimes oceur in the spaces between the primary ribs. The 
wings are also marked by two sets of raised lines, but on the posterior wing 
the radiating set is most prominent, while on the anterior wing the concentric 
set is strongest. The left valve is exactly like the right, except that the notch 
below the anterior ear is shallower. 
Length from beak to ventral margin -66 (100) ; length of hinge-line *55 (83) ; 
convexity of right valve -20 (30) ; antero-posterior dimension -66 (100). Numl 
ber of concentric lines in one-tenth of an inch, 16. The adult size of the 
species seems to be about one inch in length and breadth. 
Ranges from the base of the yellow sandstones into the base of the Burling¬ 
ton limestone. 
Aviculopecten occidentals, n. sp.—Shell small, appressed; hinge-line 
equal to greatest width ; anterior and posterior umbonal ridges at right angles, 
and straight to the middle of the shell extremities, between which the pallia! 
1863.] 
