Lamellibranchiata. 311 



actinopteria iota. 



Actinopteria iota, Hall. Pal. N. Y., vol. v, pt. 1. Unpublished. 



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 some- 

 what 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. 



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 extrem- 

 ity more produced. 



Formation and locality. In the lower part of the Chemung group 

 at Ithaca, X. Y. 



Actinopteria kappa. 



Actinopteria kappa, Hall. Pal. N. Y., vol. v, pt. 1. Unpublished. 



Shell of medium size, rhomboidal ; body narrowly ovate, oblique at 

 an angle of less than 45°; length one-third greater than the height; 

 anterior margin oblique, rounded into the broadly curved basal 

 margin ; posterior end abruptly rounded. Left valve depressed 

 below, convex from the middle upward. Right valve unknown. 

 Hinge-line straight, equal to the height of the valve. Beak sub- 

 anterior, prominent, arching over the hinge-line. TJmbonal region 

 moderately gibbous. Ear short, oblique, rounded anteriorly, defined 

 by a distinct byssal depression. Wing triangular, joining the body 

 nearly two-thirds of the length from the beak ; margin oblique, 

 concave ; extremity produced, acute. 



