LAMELLIBRA Nt 'III. I TA. 1 27 



• ACTINOPTERTA [OTA, 11. s|). 

 PLATE LXXX1V, PIG 7 



Shell of medium size, rhomboidal ; body broadly ovate, oblique ;it 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 stria?, 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, ami hinge- 

 line about 3(1 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. 



