266 Thirty- fifth Eeport on the State Museum. 



Pterikopecten" conspectus. 



Pterinopecten conspectus, Hall. Pal. N.Y., vol. v, pt. 1. Plates and Explana- 

 tions : PL 17, figs. 17-21. Jan., 1883. 



Shell of medium size, sub-rhomboidal ; moderately oblique in young 

 shells, scarcely oblique in older ones ; length and height about 

 equal, the length usually a little greater ; pallial margins regularly 

 rounded, straighter posteriorly, and merging into the ear without 

 definite limitation. Left valve moderately convex. Eight valve 

 nearly flat, narrower and oblique, with a deeper* byssal sinus. 

 Hinge-line straight, nearly central, equaling, or a little greater 

 than, the length of the shell. Beak sub-acute, anterior to the 

 center of the hinge-line, directed slightly forward. Umbonal region 

 somewhat prominent, subtending an angle of about 75°. Ears 

 triangular. Posterior one much the larger, not distinctly defined 

 on the valve ; margin slightly concave ; extremity rectangular or 

 somewhat acute. Anterior ear small, distinctly defined by a 

 rounded sulcus ; margin convex ; extremity rounded or sub-angular. 

 Byssal sinus moderate in the left valve ; deep and angular in the 

 right valve, as seen in the specimen described. 



Test of the left valve marked by comparatively few, strong, 

 rounded radii, with intermediate smaller ones, crossed by fine con- 

 centric striae of growth, and strong undulations which interrupt 

 the continuity of the radii. Eight valve marked by numerous sub- 

 equal radiating striae which are somewhat obsolete near the beak, 

 and the umbonal region is marked by some strong concentric 

 wrinkles. The ears present, in a less degree, the same ornamenta- 

 tion as the body of the shell. Ligamental area simple. 



A mature specimen is 27 mm. in length and height, and the hinge - 

 line 28 mm. 



This species differs from P . clignatus in being less oblique, the an- 

 terior ear less extended, and the radii sharper and more interrupted. 

 It differs from P. Imtus and P. Hermes in the less obliquity and the 

 stronger surface markings. It differs from Aviculopecten (Pterina ?) 

 invalidus, which is similar in general aspect, in being wider, and 

 the margin of the posterior ear less concave. 



Formation and localities. In the Hamilton group at Norton's 

 Landing, Cayuga lake, and shores of Skaneateles lake, N". Y. 



