226 Thirty-fifth Repoet on the State Museum. 



inclining to angular, distance between them greater than the strise 

 themselves ; the evidence of the implication of intermediate strise is 

 obscure ; the concentric lines are more distant and sharper, leaving 

 the radii in the cast distinctly crenulate. 



Formation and localities. In the Hamilton group at Fultonham, 

 Schoharie county ; shore of Cavuga lake, and Darien, Genesee county, 

 N. Y. 



Aviculopecten lautus. 



Amculopecten lautus, Hall. Pal. N. Y., vol. v, pt.'l. Plates and Explana- 

 tions : PL 3, figs. 16, 17. Jan., 1883. 



Shell obliquely ovate, height equal to the length, valves depressed, 

 convexity of right and left valves sub-equal. Hinge-line straight, 

 length about one-fifth less than the height of the shell, or in some 

 specimens longer, extending as far as the anterior margin of the 

 valve. Beaks depressed, obtuse, anterior to the center of the hinge- 

 line. Ears sub-equal, triangular, flat, mucronate at the extremities, 

 margins concave except in the anterior ear of the right valve, which 

 is convex; defined by the umbonal carinas, and by the absence of rays 

 on the posterior slope. Byssal notch in the right valve angular, 

 deep, continuing to the beak as a sulcus which separates the ear 

 from the umbo. The right valve, though very similar to the left, 

 is not so high, and the anterior ear differs in form from the corre- 

 sponding one in the left valve. 



Test thin, ornamented by about 90 sharp rays, with concave in- 

 terspaces having an equal number of intermediate finer rays, and 

 crossed by numerous regular, sharp concentric striae. The markings 

 on the ears are similar to those on the body, but less strong. 



The left valve of one specimen has a height of 23 mm., length 

 24 mm., hinge-line 23 mm.; the right valve of the same has a height 

 of 22 mm., and a length of 24 mm. A larger specimen is 29 mm. 

 in height, with an equal length. 



This species resembles A. exacutus in outline, but differs in the lesser 

 convexity and obliquity of the valves ; the beaks are not prominent 

 and the surface characters are finer and more delicate. Young indi- 

 viduals of A. scabridus may be distinguished from this species by the 

 more rounded and obtuse beaks, and rugose rays, which are usually 

 absent on the ears. A. formio differs by its obliquity and the inequality 

 of the ears, and the much stronger striae. 



Formation and localities. In the shales of the Hamilton group, at 

 West Bloomfield, Ontario county, and York, Livingston county, N. Y. 



