Lamellibranchiata. 305 



A left valve has a length of 13 mm., height 10 mm., and hinge- 

 line 12 mm. A large right valve has a length of 15 mm., height 

 12 mm., and hinge-line 15 mm. 



This species differs from A. tenuistriata in its more oblique body, 

 comparatively longer hinge-line, and more closely arranged and 

 stronger radii. 



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

 near Ithaca, N. Y. 



ACTINOPTERIA TENUISTRIATA. 



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 Unpublished. 



Shell small, sub-quadrate ; body short ovate, oblique at an angle of 60° 

 with the hinge-line ; length about one-fifth greater than the height ; 

 anterior margin below the sinus nearly vertical, and then making a 

 broad curve along the base ; posterior margin broadly curved. Left 

 valve regularly convex below the middle, gibbous on the umbo. 

 Right valve smaller, nearly equally convex. Hinge- line straight, a 

 little greater than the height of the valve. Beaks at about the 

 anterior third of the hinge-line prominent, obtuse, rising above 

 the hinge. Umbonal region gibbous and ample, subtending nearly 

 a right angle. ' Ear small, defined by a distinct sinus and byssal 

 depression, rounded at the extremity. Wing small, triangular, 

 joining the body below the middle of its length, not strongly 

 limited ; margin gently concave ; extremity acute. 



Test thin, marked by fine concentric striae, and filiform radiations 

 with wider interspaces, which are marked by extremely slender 

 intermediate striae. On the anterior side the radiating lines are 

 finer, and on the cardinal margin of the wing they are stronger. 

 The right valve is marked only by elevated concentric striae, and 

 the wing by fine radiations, which become stronger toward the 

 cardinal margin. 



One specimen has a length of 16 mm., height 13 mm., and hinge- 

 line 14 mm. 



This species is distinguished from A. perstrialis by its erect and 

 more nearly quadrate form, shorter ear, less extended wing with less 

 concave margin, and more distinct, finer striae. 



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

 at Ithaca, .N". Y. 



[Sen. Doc. No. 38.J 39 



