304 Thirty-fifth Report on the State Museum. 



lines, which indicate the presence of radii upon the original surface. 

 The wing is marked in a similar manner by strong bands, which 

 pas's over the hinge-margin, and it also shows two or three inter- 

 rupted radiating lines, like those on the posterior part of the body 

 of the shell. 



The specimen described has a length of 11 mm., height 13 mm., 

 and hinge-line 10 mm. 



This species is allied to A. decussata and A. Boydi, having the wing 

 characteristic, of the former ; but it is a proportionally shorter form, 

 and the surface markings are quite unlike the right valve of any of 

 the forms at present known. 



Formation and locality. In shales of the Hamilton group, on the 

 shores of Oanandaigua lake, N". Y. 



ACTINOPTERIA PERSTRIALIS. 



Actinopteria perstrialis, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explana- 

 tions : PI. 23, figs. 2, 7. Jan., 1883. 



Shell small, sub-rhoinboidal ; body sub-ovate, axis slightly curved 

 ' and oblique at an angle of about 45° with the hinge; height about 

 three-fourths the length of the body ; basal margin broadly rounded ; 

 posterior margin abruptly curved. Left valve regularly convex, 

 moderately gibbous at the umbo. Right valve depressed -convex be- 

 low, more convex above. Hinge-line straight, length equal to the 

 length of the body. Beaks sub-anterior, in the left valve prominent 

 and rising above the hinge ; in the right valve the beak extends to 

 the hinge-line. Umbonal region moderately gibbous in the left 

 valve, convex in the right, subtending nearly a right angle. Ear 

 short, separated from the body by a marked byssal depression ; ex- 

 tremity rounded. Wing narrow, triangular, joining the body mid- 

 way between the beak and the posterior extremity, not distinctly 

 defined ; margin concave ; extremity produced and acute. The 

 right valve is less distinctly auriculate in front; the anterior 

 extremity acute ; the wing is larger and the margin less abruptly 

 concave. 



Test thin, marked by fine concentric striae which are more con- 

 spicuous and equi-distant on the right valve. The left valve is 

 marked with fine, closely arranged radii, which are strongest on the 

 upper margin of the wing. The body of the right valve shows only 

 sharp, distinct, concentric striae; the wing is marked by a few rays 

 in the lower part, and by stronger radii along the hinge-line, which 

 are cancellated by the concentric striae. The auricle is radiated, and 

 cancellated in the same manner. 



