LAMELLIBRA.NCHS. 129 



near which it seems to be a little gaping; base somewhat 

 straightened, or even a little sinuous in outline, just, in front of 

 the middle, at the termination of a broad, very shallow con- 

 cavity extending obliquely downward and backward from the 

 umbonai region; behind this rather prominent, thence ascend- 

 ing obliquely, with a slightly convex outline, to the truncated 

 posterior margin. Posterior umbonai elopes very prominently 

 rounded above, and continued as a low, undefined ridge, ob- 

 liquely backward and downward; posterior dorsal slope, above 

 the umbonai ridge, with an oblique, shallow, rounded sulcus, 

 extending from the back part of the beaks to the middle of the 

 truncated margin behind. Surface marked with fine lines of 

 growth and small, irregular, concentric wrinkles, which latter 

 are not defined on the posterior dorsal region above the um- 

 bonai ridge; crossing these are the usual radiating rows of 

 minute granules. ( Meek. ) 



Horizon and localities- Upper Carboniferous, Upper Coal 

 Measures: Kansas City. 



Allorisma subcuneatum MEEK & HAYDEN. 



Allorisma subcuneatum Meek & Hayden , 1853: Proc. Acad. Nat. Sci., 



Phila., p. 263. 

 A lloris ma ensiformis Swallow, 1863: Trans. St. Louis Acad. Sci., vol. I, 



p. 656. 

 Allorisma subcuneatum Meek & Hayden, 1864 : Pal. Upper Mo., p. 37, 



pi. i, figs. JOa-b. 



Allorisma subcuneatum Geinitz, 1866: Carb. und Dyas in Nebraska, p. 76. 

 Allorisma subcuneatum Meek. 1872: U. S. Geol. Sur. Nebraska, p. 221, pi. 



ii, figs. 13a-b. 



Shell large, two or three times as long as high, with great- 

 est breadth in front of the middle, gaping slightly behind. Up- 

 per border nearly straight, flattened immediately behind the 

 beaks so as to form a long lanceolate area, with subangular 

 margins ; between these angularities and the low, scarcely de- 

 fined umbonai ridges there is a narrow, shallow depression in 

 each valve. Basal margin nearly parallel to dorsal, slightly 

 curved. Anterior border short, regularly rounded, a little gap- 

 ing. Beaks large, prominent, incurved, and placed well for- 



G 10 



