172 University Geological Survey of Kansas. 



towards the posterobasal margin, thus leaving the compressed 

 postero-dorsal region comparatively smooth. ( Muscular and 

 pallial impressions unknown.) Length, about 2 inches ; height, 

 1 inch ; convexity, 0.75 inch." 



Range and distribution : Upper Coal Measures ; Topeka. 



Our specimens differ somewhat from those figured in having 

 the sides less depressed near the beaks and ventral margin ; they 

 having shells a trifle thicker than the description calls for. 



CHJENOMYA. 



Meek, Pal. Upp. Mo., p. 42, (1864). 



Chsenomya leavenworthensis. Plate XIX, figs. 3-3b. 



Allorismaf leavemvorthensis Meek and Hay den, Proc. Acad. Nat. Sci. 



Phil. 1858, p. 263. 

 Chcenomya leavenworthensis Meek and Hayden, Pal. Upp. Mo., p. 43, 



pi. ii, ff. la-c, (1864); etc. 



Meek and Hayden's description: " Shell subcylindrical ; 

 anterior side rounded, a little compressed and apparently 

 entirely closed ; posterior side long, truncated, and very widely 

 gaping, the margins being even a little reflexed. Base nearly 

 straight, or slightly convex in outline, rounding up gradually 

 in front, and very abruptly behind ; dorsal side concave in out- 

 line from the beaks to its elevated posterior extremity, and 

 nearly parallel to the base. Beaks rather depressed, somewhat 

 flattened, incurved, nearly or quite touching, and located about 

 half way between the middle and the anterior end. Surface 

 marked by fine lines of growth, and a few irregular, nearly 

 obsolete concentric undulations, which curve up abruptly be- 

 hind, parallel to the truncated posterior margin. Crossing these, 

 the radiating rows of minute granules may be seen by the aid 

 of a good lens, on well-preserved specimens. Internal casts of 

 this species show quite distinctly the scar of the anterior ad- 

 ductor muscle, which is oval, and located near the buccal 

 margin, with its longer axis nearly at right angles to that of the 

 shell. At its upper extremity the small oval pedal scars are also 

 well defined in both valves. The posterior muscular impres- 

 sions broad, oval, and rather faintly marked; from near the 

 middle of the under side the pallial line descends with a gentle 



