144 
PALEONTOLOGY OF NEW YORK. 
the limiting furrow distinct; the fold gentle and the upper part of the wing 
flat or slightly convex; margin obliquely truncate, concave just below the 
hinge ; extremity slightly produced. 
Surface marked by fine uniform radii on the body and wing, which are 
nearly obsolete on the anterior end, and sometimes interrupted on the body 
by varices of growth; also by fine concentric striae which are acutely 
recurved over the angular posterior slope of the body, and crowded into 
fascicles at irregular intervals, producing an undulated appearance. 
Interior unknown. 
A large left valve has a length of 52 mm., height 28 mm., and hinge-line 
36 mm. A right valve in the same association has a length of 40 mm., 
height 20 mm., and hinge-line 33 mm. 
This species somewhat resembles P. trigonalis, but the posterior extremity is 
more produced, and the wing more obliquely truncate on the margin. The 
right valve in general aspect resembles the right valve of P. alata, but the left 
valve is very dissimilar. The distinguishing characters are its large rhomboidal 
form, extreme gibbosity and arcuation of the left valve. 
Formation and locality. In a compact sandstone of the Upper Chemung group, 
in the lower beds as seen at Warren, Pa. 
Ptychoptekia spatulata, n. sp. 
PLATE LXXXV, FIG. 20. 
Shell large, elongate, rhomboidal; body sub-elliptical, oblique at an angle of 
about 30° with the hinge; length more than one-third greater than the 
height; ante-byssal margin oblique, gently curving into the sinus, thence 
extending into the broadly curved basal margin; posterior end rectangularly 
or acutely recurved. 
Left valve moderately convex, slightly gibbous above. Right valve 
depressed-convex, more sub-angular along the post-cardinal slope, and smaller 
than the left. 
