LAMELLIBRANCHIA TA. 
137 
Ptychopteria Spio, n. sp. 
PLATE LXXXV, FIG. 19. 
Shell of medium size, rhomboidal; body elongate-ovate, oblique to the hinge¬ 
line. at an angle of about 30°; length considerably more than one-third 
greater than the height; ante-byssal margin curving into a shallow sinus; 
ventral margin broadly rounded; posterior margin abruptly recurved. 
Left valve regularly and moderately convex, gibbous on the umbo. Right 
valve unknown. 
Hinge-line straight, greater than the height of the valve. 
Beak in front of the anterior third, moderately prominent and scarcely 
rising above the hinge. 
Anterior extremity narrowly acute. Wing very obliquely truncate, joining 
the body near the posterior extremity; the furrow and fold separating it from 
the body are only moderately developed; extremity not produced. 
Test thin, marked by fine undulating radii which are obsolete on the 
anterior side; also by concentric striae which are prominent and lamellose on 
the anterior. 
Interior unknown. 
The specimen described has a length of 35 mm., height 20 mm., hinge-line 
24 mm. 
This species differs from P. Eucrate in its comparatively greater height; it is 
less gibbous in the left valve, the posterior end not angularly produced, the 
byssal depression less conspicuous, and the radii finer. It differs from P. Sao 
in its lesser gibbosity, greater obliquity of the wing margin, and the generally 
subdued characters of the surface markings. 
Formation and locality. In a conglomerate of the Chemung group, Panama, 
Chautauqua county, N. Y. 
18 
