400 Thibty-fifth Report on the State Museum. 



Formation and localities. In the Chemung group at Franklin, 

 Delaware county ; and a right valve referred to this species is from a 

 point four miles above Chenango Forks, Chenango county, N. Y. 



BYSSOPTERIA, Hall. 



Byssopteria radiata. 



Byssopteria radiata, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : 

 PL 32, figs. 21, 22 ; pi. 80, fig. 11. Jan., 1883. 



Shell large, wide-triangular, alate posteriorly; body undefined; 

 length about five-sevenths of the height ; anterior margin vertically 

 truncate the entire height of the shell ; basal and posterior margins 

 broadly rounded. Valves sub-equal, depressed-convex on the basal 

 and post-basal sides, sub-angularly gibbous on the umbo and along 

 the anterior side. Hinge-line straight, less than the length of the 

 shell. Beaks anterior, acute, elevated, and directed forward . An- 

 terior end sub-nasute. 



Test marked by strong, sub-equal, rounded radii which are wider 

 than the interspaces, often bifurcating below the middle of their 

 length, and on the outer portion of the undefined wing they are fas- 

 ciculate and finer. Entire surface marked by striae of growth which 

 become elevated into fascicles toward the margins. 



A right valve has a length of 55 mm., and height 72 mm. A left 

 valve measures 54 mm. in length, and 79 mm. in height. 



This species is unlike any Pectinoid or Aviculoid form described in 

 this volume, and has somewhat the aspect of several species of Am- 

 bon ychia from the lower rocks, although probably very distinct in 

 its generic relations. 



Formation and locality. In the Upper Chemung group at Mansfield,. 

 Tioga county, Pa. 



