138 University Geological Survey of Kansas. 



or less in breadth. Beaks small, very oblique, not projecting 

 beyond the cardinal margin, and located so near the anterior 

 extremity as often to appear very nearly terminal. Surface 

 rather smooth, but showing fine concentric lines, which in well- 

 preserved specimens are sometimes crossed by very fine, ob- 

 scure traces or radiating striae that curve upward on the 

 posterior dorsal region." 



Range and distribution : Upper Coal Measures ; Kansas City, 

 Topeka, Turner, Lawrence. 



Myalina subquadrata. Plate XVI, figs. 10, 10b. 



My aim a subquadraia Shumard, Geol. Surv. Mo., p. 207, pi. C, f. 17, 

 (1855); Meek, Fin. Rep. U. S. Geol. Surv. Neb., 202, pi. iv, f. 12, pi. 

 ix, f. 6(1872); etc. 



Meek's description : " Shell large and thick, oblong or sub- 

 quadrate, the height being greater than the antero-posterior 

 diameter ; right valve nearly flat ; left convex, both somewhat 

 compressed and alate above and behind the umbonal promi- 

 nence. Hinge line nearly straight, about equaling the greatest 

 breadth of the valve, and ranging at right angles to the vertical 

 axis ; the basal margin regularly rounded ; posterior margin 

 nearly vertical, rounding into the base below, a little sinuous 

 above the middle, and intersecting the hinge above at very 

 nearly right angles; anterior margin thickened within, round- 

 ing into base, thence rising nearly vertically with a broadly 

 rounded concavity mainly above the middle. Beaks terminal 

 and directed forward. Cardinal plate or area usually rather 

 broad, with cartilage furrows distinctly defined. Surface of 

 the left valve marked with fine concentric striae, and stronger 

 imbricating lamellae of growth. These markings are much less 

 distinct on the right valves." 



Range and distribution: Kansas City, Melvern (Osage 

 county), Topeka, Lawrence. 



This species can readily be distinguished from the previous 

 by its much larger size, by the hinge forming about a right angle 

 with the vertical axis, and by the sinuosity or at least straight 

 manner in which the margin approaches the posterior end of the 

 hinge. 



