LAMELLIBRANCHIATA. 127 



• ACTINOPTERIA KITA, 11. Sp. 

 PLATE LXXXIV, FKi. 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 gib))ous, 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 tine 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 -SO mm. in length, 22 mm. in height, and hinge- 

 line about oO mm. 



This form resembles A. theta, i)ut 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. 



