NATURAL SCIENCES OF PHILADELPHIA. 453 



to the posterior margin, 0-50 inch ; length of hinge, 0-35 inch ; number of 

 striae in 0.10 inch near the ventral margin, about 13. 



Named in honor of Dr. D. D. Owen, the well known Western geologist. 



Locality andpositon. Near Warsaw, Illinois. Keokuk Limestone of Lower 

 Carboniferous series. 



Aviculopecten Coxanus. Shell (left valve) rather small, very thin, com- 

 pressed, broad subtrigonal ovate in outline, exclusive of the ears, slightly 

 oblique ; anterior and posterior sides rounding from below the ears to the 

 base, which is regularly rounded ; anterior ear of moderate size, triangular, 

 and flattened, so as to be quite distinct from the umbonal slope, separated from 

 the margin below by a broad, subangular sinus; slightly rounded at the ex- 

 tremity, and marked by about eight small radiating costae, which are crossed 

 by smaller and less regular marks of growth ; posterior ear of nearly the same 

 size as the other, flattened, but not very distinct from the umbonal slope, 

 separated from the posterior margin by a regularly rounded, moderately deep 

 sinus acutely pointed at the extremity ; hinge a little less than the breadth 

 of the shell, and ranging nearly at right angles to its longer axis ; beak com- 

 pressed, scarcely projecting beyond the cardinal margin, and located very 

 slightly in advance of the middle. Surface ornamented by small, simple, 

 depressed, rigid costae, which alternate in size, the smaller ones dying out at 

 various distances between the margin and the umbo. (Right valve unknown. ) 



Length, or transverse diameter, 0*51 inch ; height, from base to hinge, 

 0-53 inch ; convexity (of left valve) 0-05 inch. 



Dedicated to Edward T. Cox, Esq., of the Geological Survey of Kentucky. 



Locality and position. Adams county, Illinois, dark bituminous Shale of 

 Coal Measures. 



Aviculopecten Burlingtonensis. Shell of about medium size, very thin and 

 fragile, suborbicular, slightly wider than long, broadly and regularly rounded 

 on the ventral margin, more narrowly rounded near the middle on each side, 

 thence sloping towards the beak at an angle of about 100 ; hinge straight, 

 between two-thirds and three-fourths as long as the transverse diameter of 

 of the valves, and ranging at right angles to their longitudinal axis. Left 

 valve much compressed ; anterior ear of moderate size, fiat, subtriangular, the 

 anterior side being shorter than either of the others, and rounding somewhat 

 into the hinge, defined by a broad rectangular sinus at its base ; posterior 

 ear flat, separated from the border below by a wide, rather deep subangular 

 sinus, and terminating in an angle of about 45 9 ; beak compressed, and located 

 a little in advance of the middle of the hinge. Surface ornamented by eighty to 

 ninety small, nearly equal, radiating costae, which increase by implantation, 

 and about equal the breadth of the depressions between. Costse crossed by 

 numerous very regular, undulating, and distinctly imbricating, concentric- 

 laminae of growth, which become closely arranged, and sharply elevated 

 on the ears, where the radiating ribs are not developed. (Right valve 

 unknown.) 



Diameter, from the ventral border to the hinge, about 2-18 inches ; do. from 

 the anterior to the posterior side, 2-30 inches ; convexity, near 0-30 inch ; 

 length of hinge, 1-63 inch; number of radiating costae in 0.40 inch near the 

 ventral margin, 10 to 12 ; number of concentric imbricating lamellae in same 

 space, about 18. 



Locality and position. Burlington, Iowa. Burlington Division of the Lower 

 Carboniferous series. 



Aviculopecten Koninckii. Shell large, subcircular, rather compressed, 

 wider parallel to the hinge than the diameter at right angles to the same ; 

 broadly rounded on the pallial margin, and more narrowly rounded on each 

 side a little below the middle. Hinge straight, apparently rather less than 

 the greatest breadth of the valves below, and ranging very nearly at right 



I860.] 



