Maryland Geological Survey 455 



from the other species of this genus by its great breadth. A part of the 

 postero-dorsal extremity and of the beak is broken ofl". 



Occurrence. — Oriskany Formation, Eidgely Member. Hancock. 

 Collection. — Maryland Geological Survey. 



[Ohern.] 

 Family PTERIIDAE 



Genus ACTINOPTERIA Hall 



Actinopxeria communis (Hall) 

 Plate LXX\a, Figs. 2-4 



Avicula communis Hall, 1859, Nat. Hist. N. Y., Pal., vol. ill, p. 286, pi. lii, 



figs. 1-7; pi. liii, figs. 1, 4, 6, 1861. 

 Actinopteria communis Clarke, 1900, Mem. N. Y. State Mus., No. 3, vol. lii, p. 



34, pi. iv, figs. 1, 2. 

 Actinopteria communis Waller, 1903, Pal. N. J., vol. ill, p. 292, pi. xxxi, fig. 21. 



Description. — " Shell obliquely ovate ; the left valve gently convex in 

 the middle, and becoming gibbous towards the beak, which in the young 

 shell is narrow and projecting above the hinge-line; right valve flat or 

 gently concave in the middle and below, and becoming slightly convex on 

 the umbo; anterior side gently curving to the base which is broadly 

 rounded, the curvature of the posterior side being more abrupt : anterior 

 wing small, trigonal, obtuse at its extremity, strongly defined from the 

 body of the shell : posterior wing three times as long as the anterior wing, 

 obtusely or subacutely pointed, extending more or less beyond the margin 

 of the shell, concave on the outer or lateral margin, its junction with the 

 body of the shell not strongly defined. 



" Surface of the left valve marked by slender, sharply defined, rounded 

 radii, the principal of which are distant from two to four or five times their 

 width, and the spaces occupied by one, two or three finer interstitial radi- 

 ating strice (these radii are but faintly, and sometimes not at all per- 

 ceptible on the posterior wing, except along its upper margin, while they 

 are not seen on the anterior wing) ; concentrically marked by fine lamellose 

 strige, which, in the more perfectly preserved surfaces, are elevated and sub- 

 imbricating : these strige are usually conspicuous on both the anterior and 

 posterior wings. Surface of the right valve marked by broader and 

 scarcely elevated radii and less defined concentric striaa.'' Hall, 1859. 



