Bkkde.] Carboniferous Invertebrates. 121 



Aviculopecten hertzeri. Plate XIII, figs. 8, 1, lb. 



Aviculopecten [Streblopteriat) hertzeri Meek, Proc. Acad. Nat. Sci. 

 Phil.. L871, i'. 61; Pal. Ohio, n, p. 330, pi. xix, ff. 13a-c, (187.")). 

 •ulopecten In rtz< ri Herrick, Ball. Den. Univ., n, p. 25, pi. i, ff. 5, 10. 



Meek's description : " Shell usually under medium size, 

 higher than wide, rather compressed, the right valve being 

 nearly flat, and the left only moderately convex ; subovate in 

 general outline (exclusive of the ears), with a slight backward 

 obliquity, caused by the greater prominence of the anterior 

 margin ; basal outline semicircular and rounded regularly into 

 the rather prominently rounded anterior margin ; posterior 

 margin less prominent than the anterior, and forming a longer 

 and more or less gentle curve from the posterior ear into the 

 base.; hinge distinctly shorter than the antero-posterior di- 

 ameter of the valves ; posterior ear in both valves very small, 

 llattened, very obtusely angular, and much shorter than the 

 margin below from which it is only separated by a slight sinu- 

 osity, though it is well defined from the umbo ; anterior ear of 

 each valve distinctly larger than the posterior, though not 

 nearly so prominent as the anterior margin .below, rather 

 strongly compressed or flattened, so as to be abruptly separated 

 from the umbo, and in both valves defined by a distinct sinus 

 from the margin below, the sinus being deeper and more angu- 

 lar in the right valve ; beaks compressed, scarcely projecting 

 above the cardinal margin, and placed a little behind the middle 

 of the hinge, as well as that of the valves. Surface of both 

 valves elegantly ornamented by numerous, sometimes sharply 

 elevated, nearly equal, very regularly arranged radiating and 

 concentric lines, which are larger and more strongly defined on 

 the anterior ear of the right valve, particularly the radiating 

 markings, which there sometimes assume the character of small 

 costa\ while the concentric markings there in some examples 

 project as little lamellae above the hinge margin, so as to give 

 it a subtended appearance. Height of one of the largest speci- 

 mens seen, 1.32 inches ; antero-posterior diameter, 1.20 inches ; 

 convexity, about 0.18 inch." 



9— vi 



