124 PALEONTOLOGY OF NEW YORK. 



striiu, with iiik'niiediatL' liiicr line;;, and In sk-nder, lililoiia, undulatin;^-, 

 distant ravs, which an- more crowded on the anterior side, becoming finer and 

 more nnmerons at tlie juncticm of the wing with the liody, and a few nuuli 

 stronger ones along the cardinal line. Rays not present on the ear, wliicli is 

 marked only by the crowded concentric striae The concentric stria^ crenu- 

 late the rays and liend backward in tlie interspaces, prodncing a beautifully 

 cancellated surface. 



The right valve shows two oblique lateral folds or teeth posterior to the 

 beak. 



A right valve has a length of 25 mm. parallel to the hinge, height 28 mm., 

 iiingc-line about 34 mm. An imperfect left valve has an approximate length 

 of 22 mm., iieight 24 mm., and hinge-line 33 mm. 



This species is distinguished by its erect, orbicular rorm. great extension of 

 hinge-line, and marked surface characters. 



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

 N. Y. 



ACTINOPTERIA ETA, 11. sp. 



I'LATK LXXXIV, FIGS. S-11. 



Shell of medium size, rhomboidal ; body broad and short-ovate, oblique at an 

 angle f)f about 45° : length about one-fourth greater than the height ; anterior 

 margin below the sinus nearly vertical, curving gradually into the broad 

 base ; posterior side regularly rounded. 



Left valve regularly convex below, moderately gibbous above. Ilight 

 valve smaller, depressed-convex below, gently convex above. 



Hinge-line straight, length greater than the height of the shell. 



Beak in Ihc left valve sub-anterior, prominent, arching over the hinge: in 

 the right valve subdued, scarcely rising above the hinge-line. UmlMnial 

 region gibbous in the left valve, subtending an acute angle. 



Ear, in the left valve rounded at the extremity, slightly oblique, defined by 

 a distinct byssal depression. In the right valve the oar is larger and flat. 



