LAMELLIBRAiiTCHIATA. 227 



AviCULOPECTEN EUG^ISTRIATUS. 



Lima rugcestriata, Hall. Geolog. Surv. N. Y.: Rep. Fourth Dist., p. 264. 1843. 

 Aviculopecten rugcestriatus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and 

 Explanations : PL 7, figs. 8-11. Jan,, 1883. 



Shell longitudinally ovate, oblique ; more convex in front ; height 

 one-fourth greater than the length ; outline oblique-ovate, with 

 the posterior margin depressed convex ; the anterior margin more 

 convex, and the base abruptly rounded. Valves convex, very similar, 

 except that the right valve shows an acute byssal sinus. Hinge- 

 line short, straight, length more than one-half the length of the 

 shell. Beaks acute, prominent, anterior to the middle of the hinge. 

 Ears small, broad, triangular ; posterior one a little the larger, mar- 

 gin slightly concave ; anterior ear defined by a distinct sulcus, 

 which is narrow and deep in the right valve, margin convex ; byssal 

 sinus deep and acute. The posterior ear is less distinctly limited in 

 the right valve. 



Test near the beaks ornamented by fine filiform rays, which are 

 crossed and crenulated by sharp, concentric striae. Below the mid- 

 dle of the shell, the rays become large rounded plications, increasing 

 by implantation or bifurcation, and the regular concentric striae are 

 stronger, distinctly crenulating the rays, becoming foliate, and giv- 

 ing the surface a rugose appearance. The rays and concentric lines 

 are present on the ears . 



Two left valves have a height of 35 mm., and 22 mm.; length 29 

 mm. and 18 mm.; the hinge-line 16 mm. and 10 mm., respectively. 

 A right valve of nearly the same proportions has a height of 33 mm., 

 length 25 mm., and hinge-line 17 mm. 



This species is distinguished from A. duplicatus by its comparatively 

 greater height, the obliquity of the valve, and the acute beaks ; the 

 surface characters of the two are very similar. A. cancellatus is more 

 circular in outline, and the anterior ears are larger than the posterior 

 pair . 



Formation and localities. Shales of the middle Chemung group, 

 Philipsburg, Rockville and Hobbieville. Alleghany county, N. Y. 



