Lamellibrajstchiata. 283 



the middle, also slopes in a direct line to the beak. Left valve 

 moderately convex; the greater convexity about one- third the 

 height of the shell from the beak. Eight valve nearly flat, de- 

 pressed-convex above. The right and left valves are unlike. 

 Hinge line straight, central, length about two-thirds the length 

 of the shell. In several specimens referred to the right valve, 

 the length of the hinge is nearly equal to the length of the 

 valve. Beak of left valve acute, erect, prominent. Beak of right 

 valve depressed, obtuse, not rising above the hinge-line. Um- 

 bonal region of left valve distinctly defined, subtending a right 

 angle. Ears of left valve triangular, defined by shallow but 

 distinct sulci. Margin of anterior ear convex, with a shallow sinus 

 at the base. Posterior ear the larger ; margin concave, with a com- 

 paratively broad sinus. The extremities of the ears in the right 

 valve are acute. Byssal sinus deeper and more angular in the right 

 valve . 



Surface of left valve marked by numerous rounded or sub-angular, 

 alternating rays, with somewhat wider interspaces, crossed by sharp, 

 elevated, concentric strige ; the ears show the same markings. Eight 

 valve marked by obscure radii, which are stronger on the ears. 

 Ligamental area with numerous narrow cartilage-pits. 



A large left valve has a length of 47 mm., height 42 mm., hinge- 

 line 29 mm. Another individual measures 27 mm. in length, 26 mm. 

 in height, hinge-line 18 mm. A right valve referred to this species 

 has a length of 20 mm. and a height of 18 mm., hinge-line 17 mm. 



This species differs from any known form of Crenipecten" ; it is like 

 Aviculopectek in external form and surface characters, and resembles 

 the recent genus Pecten". Mr. Meek compares this species with 

 Aviculopecten Coxanus, Meek and Worthen, from the coal measures 

 of Illinois and Nebraska. It is evident that the crenulations of the 

 hinge have not been previously observed. The right and left valves 

 have not been found in connection, but their association, and the 

 absence of similar forms in the same beds, render the identity nearly 

 certain. Except in the hinge crenulatious this form has no other re- 

 lations with the genus Orenipecten, and it may be found to belong 

 to some genus yet undescribed, which will include other species now 

 placed with the carboniferous forms of Aviculopecten. In the 

 original description of that genus, McCoy has not indicated the in- 

 timate structure of the hinge, and it is not improbable that there are 

 several generic types among the species included in the carboniferous 

 forms of Ayiculopecten. 



Formation and locality. In the Waverly sandstone near Newark, 

 Ohio. 



