LAMKLLMRANCHIATA. 21 



d'Orbigny), the valve is more convex, beak more obtuse, and the c entric 



marking forms a prominent feature. 



Formation and locality. In the Chemung group at Conewango, Cattaraugus 

 county, N. Y. 



A.VICULOPECTEN PLENUS. 



PLATE XXIV. FIG. 3. 



Aviculopecten plums. Hall. Pal. N. V.. vol. \. j.t. I. Plates and Explanations: I'!. 24, fig. :i. Jan., 1883. 



Shell sub-orbicular, sub-equilateral ; transverse axis nearly vertical to the 

 binge-line; height one-sixth less than the length, giving a marked fullness 



to the outline of the sides. 



Left valve convex, the convexity equal to one-sixth the length of the 

 shell. The point of greatest convexity distant one-third the length From 

 the heak. Right valve not observed. 



Hinge-line straight, nearly central, the length more than two-thirds the 



length of the shell. 



Beak ohtnse, situated centrally with regard to the hinge-line, and also to 

 the body of the shell; umbo rounded. 



Ears sub-equal, triangular. Posterior ear mucronate at the extremity : 

 margin deeply concave. Anterior ear acute at the extremity, and the margins 

 convex; separated from the umbo by an abruptly sloping sulcus extending 

 to the heak. 



Surface ornamented with about 130 regular, rounded, close, filiform radii, 

 crossed by very line, sharp, concentric stria'. The surface markings are 

 present on the ears, the radii distinct and stronger than on the adjacent 

 portions of the shell. The rays become more frequent ami liner from the 

 basal margin in both directions towards the ears. 



Interior not preserved in the specimen described. 



The height of the specimen is li-"i mm., length 30 nun., hinge-line 2 1 mm. 

 On the lower margin there are '.' rays in the space of 5 mm. 



