1895. | NEW YORK ACADEMY OF SCIENCES. UF 
muscles, while the third or posterior scar is minute and on some 
valves cannot be discerned, these two bands of scars, one on 
each side of the mesian line, form sets of muscle imprints 
corresponding to the two arched central scars of O. Apollonis. 
The interior of this valve is traversed by a number of ridges 
radiating from near the umbo to the anterior part of the valve. 
“Interior of the Ventral Valve (Figs. 2 h to l). There is 
muca resemblance in general aspect between the interior of the 
dorsal and ventral valves. The latter differs in the more elon- 
gated callus of the visceral cavity. the narrower scar of the 
posterior adjustor muscle, the absence of the strong lateral 
ridge beside this muscle, and the want of a division along the 
mesian line. This valve also exhibits indications of the attach- 
ment of the pedicel, and of the central adjustor muscles. The 
ventral valve also possesses a smaller, pointed depression in the 
front of the visceral cavity, which probably marks the attach- 
ment of the anterior adductor muscle. From this point, a some- 
what depressed band extends to the front of the shell. There 
are indications that the pedicel passed through a foramen in the 
hinge, coming on the hinge area below the beak, but this point 
is not clearly determinable.” 
Additional Note. The ventral valve has a pair of scars in 
front of the hinge area due to the posterior adductors, and two 
pairs of lateral muscles (adjustors) extending forward at the 
sides one-half of the length of the valve. The central scars 
form a pair subtriangular in form and placed in front of the 
middle of the valve; the outer ends are directed backward, each 
scar is double and the whole corresponds to the ventral scar of 
Obolus Apollonis, only that it is wider. There are two strong 
ridges dividing the sliding muscles from the inner cavity of the 
shell, and the border of the splanchoceele is indicated by a cury- 
ing line. 
“ Sculpture. The younger part of the shell is covered with 
minute tubercles, sloping forward, and arranged in curved rows 
which arch forward to the mesian line from each lateral margin 
of the valve, thus giving the surface a cancellated appearance; 
this cancellated or rasp-like surface does not cover the valve 
continuously, but is interrupted by arching bands of ridges con- 
centric to the umbo. The anterior part and the outer lateral 
parts of the valves have the concentric ridges only, with a few, 
faint, broken, radiating lines, visible at intervals. The cancel- 
lated lines do not always cover so large a space on the dorsal as 
on the ventral valve, but the former valve shows more distinctly 
the radiating lines outside the visceral cavity. 
Growth and Development. The growth and development of 
