LAMELLIBRANCHIA TA. 
127 
Actinopteria iota, n. sp. 
PLATE LXXX1V, FIG. 7. 
Shell of medium size, rhomboidal; body broadly ovate, oblique at an angle of 
about 45°; length about one-seventh greater than the height; anterior margin 
nearly vertical or slightly inclined for a short distance, thence curving into 
the broad base; posterior end broadly rounded. 
Left valve depressed below, regularly convex above, scarcely gibbous. 
Right valve unknown. 
Hinge-line straight, about equal to the length of the shell. 
Beak sub-anterior, prominent. Umbo moderately gibbous, subtending an 
acute angle. 
Ear comparatively short, defined by a distinct byssal depression, rounded 
at the extremity. Wing not strongly limited, extending quite as far as the 
posterior extremity of the shell; margin somewhat deeply concave in the 
middle; extremity produced and acute. 
Surface marked by concentric lamellose striae, and fine thread-like rays, 
which are crenulated and cancellated by the lines of growth both on the 
body and on the wing. 
Interior unknown. 
One of the specimens is 30 mm. in length, 22 mm. in height, and hinge¬ 
line about 30 mm. 
This form resembles A. theta , but the body is proportionally shorter, the 
hinge-line longer, the wing margin more concave and the extremity more 
produced. 
Formation and locality. In the lower part of the Chemung group at Ithaca, 
N. Y. 
