114 University Geological Survey of Kansas. 



Both these and the concentric striae are almost invisible to the 

 unassisted eye." 



"Anterioposterior diameter of a specimen a little under me- 

 dium size, 0.85 inch ; height, 0.89 inch ; length of the hinge 

 line, 0.27 inch. Specimens are sometimes found of nearly 

 double these dimensions." In some delicately preserved casts 

 there are traces of zigzag markings on the anterior of the ven- 

 tral margin of the left valve. 



Range and distribution : Upper Coal Measures ; Lawrence, 

 Topeka. 



AVICULOPECTEN. 



McCoy, Ann. Mag. Nat. Hist., 2d ser., VII, p. 171, (1851 ). 



Aviculopecten occidentalis. Plate XIII, fig. 7. 



Pecten occidentalis Shumard, Geol. Rep. Mo., p. 207, pi. c, f. 18, (1855); 

 Newberry, Ives's Colo. Expl. Exped., p. 128, (1861). 



Pecten cleavelandicus Swallow, Trans. St. L. Acad. ScL, i, p. 184, (1858). 



Aviculopecten f Meek and Hayden, Pal. Upp. Mo. (Smiths. Cont. 



Knowl., xiv), p. 50, pi. n, f. 10, (1864). 



Aviculopecten occidentalis Meek and Worthen, Geol. Surv. 111., n, p. 

 331, pi. xxvn, ff. 4-5a, (1866); Meek, U. S. Geol. Surv. Neb., p. 191, pi. 

 ix, f. 10, (1872); etc. 



Pecten missouriensis ? Geinitz, Carb. u. Dyas in Neb., p. 35, pi. n, f. 18, 



(1866). 



Meek's description: ''Shell distinctly inequivalve, not ob- 

 lique ; subovate exclusive of the ears ; lateral and basal mar- 

 gins regularly rounded ; hinge margin nearly or quite equaling 

 the greatest breadth of the valves ; cardinal plate of moderate 

 breadth. Left valve convex, with ears subequal ; anterior 

 one with distinct radiating costse, more convex, shorter, 

 and more obtuse than the posterior, as well as more defined 

 from the swell of the umbonal slope ; posterior ear flattened 

 and more angular at the extremity than the other, some- 

 times without radiating costse, but in other instances having 

 them more or less developed, each separated from the mar- 

 gin below by a rounded, rather broad, more or less deep sinus. 

 Right valve nearly flat and having the general outline of the 

 other excepting that its beak is scarcely distinct from the car- 

 dinal margin, and its anterior ear much narrower and defined 

 by a deep, sharp angular sinus. Surface of valve ornamented 



