LAMELLIBRANCHIATA. 117 



middle of the valve, extends parallel with the margin to the anterior side of 

 the umho. 



The specimen described lias a length of 37 mm., heighl 24 mm., hinge- 

 line 27 mm. 



This specimen occurs associated with A. Boydi and other allied forms, and is 

 known by the convexity of the valves, the sub-angular character of the posterior 

 slope of the left valve, the great obliquity, the proportions of length and height, 

 and the absence of radii in the cast. 



Mr. Conrad's original description of A. perobliqua is as follows : 



" Avicula perobliqua, pi. 12, fig. 1. — Obliquely sub-ovate, with radiating lines 

 "distinct only on the posterior side: dorsal line rectilinear, long and very 

 " oblique ; anterior wing short, wide, sinuous, the front margin inclining to a 

 " regular arch ; posterior extremity acutely rounded. 



" Locality — Hamilton, Madison county, N. Y. ; Upper Silurian shale. 



" A common species, very easily distinguished from others of the genera 

 " with which it is associated, by its long, very obliquely ovate outline. Casts 

 " of the interior scarcely exhibit any radiation. It is often found with connected 

 " valves." 



The radii mentioned in this description cannot be recognized in the specimen 

 which preserves only concentric striae on some parts of the surface. Mr. 

 Conrad's description may have included casts of A. Boydi, which show slight 

 traces of radiation, and occur in the same association. 



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

 Madison county, N. Y. 



ACTINOPTERIA PUSILLA, U. s]>. 

 PLATE I.XXXIV, FIG. :j. 



Shell small, sub-rhomboidal : body ovate, very oblique: length and height 

 nearly equal ; margin for a short distance on the anterior side nearly vertical. 

 broadly rounded along the base and produced on the posterior side. 



