INVERTEBRATES. 329 



separated from the margin below by an obtusely angular, or 

 somewhat rounded sinus; posterior ear compressed, longer than 

 the other, and acutely angular at the extremity, separated from 

 the margin below by a nearly rectangular notch; beak com- 

 pressed, small, and not projecting beyond the hinge margin, 

 located a little in advance of the middle of the hinge; cardi- 

 nal area inclined over towards the right, and not very wide ; 

 surface ornamented by rather small, straight, obscure, de- 

 pressed, radiating costae, crossed by nearly obsolete marks of 

 growth. Left valve more convex, and marked by more promi- 

 nent costse, which are crossed by much smaller, closely arranged 

 concentric strias. Ears and beak unknown. Greatest breadth 

 parallel to the hinge a little below the middle, 3.39 inches; 

 height, or diameter from the base to the hinge, about 3 inches; 

 length of hinge, near 3 inches. 



This fine species presents some anology, in size and general outline, to Avi- 

 culopecten concavus, of McCoy, {Synop. Carh. Foss. Ireland, tab. 15, fig. 10), but 

 may be readily distinguished by its more pointed posterior ear, and the coarser, 

 as well as more regular costse of its left valve, which is also a little convex, 

 instead of concave. In our figure, however, the costse are represented a little 

 too irregular, and too crowded on the posterior ear of the right valve. Usually 

 about eight or nine of the costse occupy a space of half an inch at the ventral 

 margin of the body of each valve. They seem always to increase by interca- 

 lation, the intermediate ones dying out between the free margin and the umbo. , 



The specific name was given in honor of Prof. L. deKoninck, the distin- 

 guished palaeontologist of Liege. 



Locality and position: Alpine, Iowa; Lower Coal Measures. 



AVICULOPECTEN INTERLINEATUS, M. and W. 



PI. 26, figs, la, 1 b. 



Aviculopecten interlineatus, Meek and Worthex, Oct., 1860. Proceed. Acad. Nat. Sci., 

 Philad., p. 454. 



Shell (left valve) rather small, compressed, broad ovate or 

 subcircular exclusive of the ears, not oblique; length and 



42 Sept. 21, 1866. 



