LAMELLIBRANCHIATA. 107 



Pterinopecten latus, l)ut it is a larger and coarser form, with the right valve con- 

 vex. The geological positions of the two species are quite different. The 

 character of the surface ornamentation distinguishes it from Pterinea prora and 

 Pterima avis. 



Formation and locality. In shales of the Chemung group, 600 feet above the 

 base of the formation, at Ithaca, N. Y. 



ACTINOPTERIA, Hall. 



ACTINOPTERIA EXIMIA. 



ri.ATE XXV, KIG. 1. 



Actinopteria exiiiiia. Hall. Pal. N. Y., voL v. pt. 1. Plato.'; and Explanations: PL 25, tig-. 1. Jan.. 18S3. 



Shell small, rhomboidal ; body falciform, very oblique ; length more than one- 

 third greater than the height; margin broadly curved along the ventral 

 side and abruptly recurved over the posterior end. 



Left valve convex. Right valve unknown. 



Hinge-line straight, less than the length of the valve. 



Beak acute, directed forward. Umbonal angle about 00'^. 



Ear short, oblique, limited by a distinct sulcus ; margin convex ; extremity 

 rounded. Wing imperfectly preserved in the specimen described, apparently 

 joining the body near the middle of the post-cardinal slope, and very .strongly 

 defined ; margin concave, extending acutely backwards ; extremity acute. 



Test marked by al)out twenty strong, elevated slender rays, with regular 

 . lamellfB of growth which are extended and bent backwards on crossing the 

 rays, producing strong semi-tubular spines. The cardinal expansions pre- 

 serve only the lines of growth. 



Interior unknown. 



The specimen described has a length of 20 mm., and height of 14 una. 



The description is made from the figure given on plate xxv, as the specimen 

 cannot be found at the time of this writing. The characters of form and surface 

 ornamentation are very characteristic, and the species is important as being the 



