16 



PECTENIDJE. 



GENUS PECTEN, Brug. 

 PECTEN NEWBERRYI, n. sp. 



Plate 4, figs. 12-15. 



Shell of moderate size, suborbicular in outline, erect and subequilat- 

 <eral, the height and length nearly equal. Valves depressed-lenticular 

 in a transverse section when united ; their surfaces depressed- con vex, 

 except along the sides of the valves near the cardinal slopes, where the 

 surface is elevated so as to form a broad, rounded, fold-like border on 

 this part ; with a broad, undefined, shallow depression separating it 

 from the body of the valve. Hinge line short; that of the left valve 

 less than half as long as the shell below ; straight or a very little slop- 

 ing outward from the apex of the valve, which is small, appressed, and 

 not projecting above the line of the hinge. Anterior side of the hinge 

 a little longer than the other, the anterior wing being rounded at the 

 extremity, more than as long again as the height above the body of the 

 valve at its widest part ; separated from the shell below by a very shal- 

 low, rounded byssal notch, and along the surface by a scarcely percepti- 

 ble groove bordering the body of the valve. Posterior wing smaller, 

 triangular, a little obtuse at the outer upper angle, and proportionally 

 somewhat higher or longer on the lateral border than the anterior wing. 

 Surface of the left valve marked, except on the fold and depression 

 bordering the cardinal slopes, by strong, flattened radii, which are vari- 

 able in strength, size, and distance, and are separated by flattened 

 interspaces, usually of greater width than the ribs themselves. The 

 surface is also marked by closely arranged, distinctly elevated, regular, 

 lamellose, concentric lines parallel to the outer margin, and coincident 

 with the lines of growth, and are slightly arched backward in crossing 

 the radii. These latter markings also cover the surface of the folds of 

 the cardinal borders and the cardinal auriculations. 



A single right valve of small size associated with a number of left 

 valves, on the same block, has the same general form and the same 

 fold-like feature of the cardinal slopes, but appears to be entirely desti- 

 tute of the radii on the body of the valve ; and the concentric markings 

 are also much less distinct and regular than on the opposite valve. The 

 anterior wing is also very small and obtusely triangular, but may have 

 been somewhat mutilated. There can be little if any doubt, however, 

 that this right valve belongs to the same species. 



This species may be readily distinguished by the peculiar fold like 

 feature of the cardinal slopes and the character of the concentric mark- 

 ings, being entirely different in these respects from any other of the 

 genus described from rocks of this age. 



