76 University Geological Survey of Kansas. 



umbonal region gibbous ; beak incurved, but scarcely passing 

 the hinge margin ; ears large, rather compressed, and provided 

 with a few large, strongly defined concentric folds, which as- 

 cend a little upon the sloping sides of the umbo and extend 

 more or less along the postero-lateral margins, but never cross 

 the shell ; surface ornamented with rather small, regular, 

 rounded costae or striae, and armed with stout, erect, long 

 spines, those along the hinge margin are more frequent, larger, 

 directed backward, with an inward curve. Some specimens 

 seem to be nearly destitute of spines. Dorsal valve concave, 

 sometimes a little flattened in the visceral region, and following 

 the curve of the other valve around the front and anterior 

 lateral margins ; ears with folds as in the other valve, and each 

 separated from the concave central region by an oblique ridge 

 or prominence ; surface without spines, but with radiating 

 striae, as in the ventral valve, and usually crossed by very ob- 

 scure concentric wrinkles and a few imbricating marks of 

 growth, particularly near the front and sides ; cardinal process 

 small but strongly prominent and bifid, while from its base a 

 slender mesial ridge extends forward to, or a little beyond, the 

 middle. " The internal markings of this valve are obscure. Pro- 

 boscis well developed, bifid, and well produced into the beak 

 of the other valve. Lateral ridges small, straight or curved 

 backward, soon disappearing ; adductor scars dim, placed well 

 to the posterior, nearly semicircular in outline ; brachial mark- 

 ings indistinct, enlarging and bending to the front at the ex- 

 tremities. A cast of the interior of the pedicle valve shows a 

 narrow, short beak, with a small depression on either side, 

 faint mesial ridge extending across the central portion of the 

 visceral area ; adductor scars long and narrow, placed close be- 

 side the ridge ; exterior to these are the linear markings of the 

 diductors. Anterior marked by fine pittings. Length of fair- 

 sized specimen, .50 mm. ; width, 70 mm. 



Range and distribution : Upper Coal Measures ; Kansas City, 

 Eudora, Lawrence, Lecompton, Topeka, Geary county, Melvern, 

 Osage county. 



The size of the costae in this species is variable, those with 



