Lamellibraxchiata. 245 



are mostly free from surface markings. Pallial line impressed, 

 continuous, situated about one-half the distance between the apex 

 of the beak and the pallial margin of the shell. Muscular impres- 

 sion elliptical, within the concavity of the valves adjacent to the 

 sulcus of the posterior ear. Hmge-ligament without marked 

 characters. 



The largest specimen has a height of 29 mm., length 30 mm., and 

 hinge-line about 23 mm. A smaller individual is 23 mm. in 

 height, 23.5 mm. in longitudinal diameter, and hinge-line measur- 

 ing 19 mm. 



This species resembles in some respects A. ignotus, and is distin- 

 guished by its transverse form, greater obliquity, larger anterior ear 

 in the left valve, rectangular beak, and more regularly alternating rays. 

 Both of these forms are remarkable for the very slight convexity of 

 the left valve. 



Formation and localities. In calcareous sandstone of the Upper 

 Chemung group, Randolph and Salamanca, Cattaraugus countv, 

 N. Y. 



LYRI0PECTE3T, Hall. 

 Lyriopecten parallelodontus. 



Lyriopectenparallelodontus,~H.A.i l Ti % MS, for Pal. N. Y., vol. v. 187,7. 



" " S. A. Miller. Cat. Amer. Pal. Foss, 



Cincinnati, 1877. 

 Lyriopecten parallelodontus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Ex- 

 planations : PI. 4, figs. 1, 2. Jan., 1883. 



Shell of medium size, sub-orbicular, not oblique ; height some- 

 what less than the longitudinal diameter; margins regularly 

 rounded. Right valve moderately convex. Left valve unknown. 

 Hinge-line straight ; anterior portion not preserved in the specimen ; 

 from the beak to the extremity of the posterior ear its length is 

 one-half the longitudinal diameter of the shell. Beak obtuse, 

 rounded, slightly oblique, anterior to the center of the valve ; 

 umbonal region ample. Posterior ear large, broad-triangular, flat'; 

 margin straight or slightly concave ; extremity rectangular. Ante- 

 rior ear not preserved. 



Test thin, marked by about 90 regular, alternating, rounded 

 radii, with concave interspaces, and crossed by fine, elevated, sharp, 

 cancellating strise; these are crowded over the posterior ear, and 

 the rays are there more numerous and less regularly alternating. 

 The mould of the interior preserves, around the margin, traces of 



