312 Thirty-fifth Beport on" the State Museum. 



Test thin, marked by fine, concentric, irregularly fasciculating 

 striae, giving an undulated appearance to the surface, and by fili- 

 form, interrupted and undulating radii, with wider interspaces, 

 which sometimes show fine intercalated rays. The radii upon the 

 wings are prominent and cancellated by the concentric striae, and 

 are obsolete upon the ear. 



The specimen has a length of 30 mm., height 20 mm., and 

 hinge-line 20 mm. 



This species differs from A. epsilon, in the greater obliquity, longer 

 hinge-line, and more distant radii. 



Formation and locality. In the lower member of the Chemung 

 group at Ithaca, "N". Y. 



PTYCHOPTEKIA, Hall. 

 Ptychopteria Proto. 



Ptychopteria Proto, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : 

 PI. 23, figs. 12, 14. Jan., 1883. 



Shell small, rhomboidal ; body narrow-ovate, oblique at an angle of 

 about 35° with the hinge-line; length more than one-third greater 

 than the height; ante-byssal margin sub-truncate, rounding into 

 the broad sinus ; base broadly rounded ; posterior end somewhat 

 abruptly curved. Left valve regularly convex below, gibbous in the 

 middle and above. Eight valve unknown. Hinge-line straight, 

 length a little greater than the height of the valve, and nearly equal 

 to two-thirds its length. Beak at about the anterior third of the 

 hinge, prominent, inclined forward. Umbo abruptly gibbous, sub- 

 tending an acute angle. Anterior end large,* rounded, limited by 

 a broad byssal depression directed backward; extremity angular. 

 Wing small, narrow-triangular, extending to near the posterior end 

 of the body ; margin scarcely concave : extremity obtuse. 



Surface marked by fine, regular, elevated radii, which are less 

 conspicuous on the wing; also by concentric striae, which are often 

 crowded and lamellose, producing a somewhat undulated character 

 of the surface. 



A large left valve has a length of 29 mm., height 18 mm., and 

 hinge-line 20 mm. A smaller specimen has a length of 20 mm. 9 

 height 13 mm., and hinge-line 14 mm. 



*In the descriptions of the species of Ptychopteria and Leptodesma, the term " auricle " 

 or " ear " is not so applicable to the anterior extension as Actinopteria and Leiopteria and 

 the term " anterior end " has been used for that portion of the shell anterior to the byssal 

 sinus. 



