LAMELLIBRANCHIA TA. 
129 
PTYCIIOPTERIA, Hall. 
Ptychopteria Proto. 
PLATE XXIII, FIGS. 12, 14. 
Ptychopteria Proto, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 23, figs. 12, 14. 
Jan., 1883. 
Shell small, rhomboidal; body narrow-ovate, oblique at an angle of about 35° 
witb the hinge-line; length more than one-third greater than the height; 
ante-byssal margin sub-truncate, rounding into the broad sinus; base broadly 
rounded; posterior end somewhat abruptly curved. 
Left valve regularly convex below, gibbous in the middle and above. 
Right valve unknown. 
Hinge-line straight, length a little greater than the height of the valve, 
and nearly equal to two-thirds its length. 
Beak at about the anterior third of the hinge, prominent, inclined forward. 
Umbo abruptly gibbous, subtending an acute angle. 
Anterior end large,* rounded, limited by a broad byssal depression directed 
backward; extremity angular. Wing small, narrow-triangular, extending 
to near the posterior end of the body; margin scarcely concave; extremity 
obtuse. 
Surface marked by fine, regular, elevated radii, which are less conspicuous 
on the wing; also by concentric striae, which are often crowded and lamel- 
lose, producing a somewhat undulated character of the surface. 
Interior unknown. 
A large left valve has a length of 29 mm., height 18 mm., and hinge-line 
20 mm. A smaller specimen has a length of 20 mm., height 13 mm., and 
hinge-line 14 mm. 
This species resembles P. sinuosa, but the anterior end is wider; the wing 
is smaller and not produced at the extremity, and the radii are coarser. These 
* In the descriptions of the species of Ptychopteria and Leptodesma, the term auricle or ear is not so 
applicable to the anterior extension as in Actinopteria and Leiopteria and the term anterior end-has been 
used for that portion of the shell anterior to the byssal sinus. 
17 
