156 University Geological Survey of Kansas. 



indistinct and ill defined. Posterior portion of the shell some- 

 what wedge-shaped. The fine concentric striae of growth are 

 most apparent on the anterior and posterior ends and along the 

 ventral margin. The interior of the shell is marked by rather 

 deep adductor scars, the anterior being situated very near the 

 anterior dorsal margin, rather broadly elliptical in outline, 

 while the posterior is situated near the posterior end of the liga- 

 ment and is much larger, rather ovate in outline. The pallial 

 line is indistinct, but seems to pass rather closely to the ventral 

 margin around to the anterior end, where it curves rather regu- 

 larly upward to the anterior adductor. There is a ridge in 

 the interior of the shell extending from the umbo obliquely 

 backward about one-half to two-thirds the distance to the pos- 

 tero-ventral margin. In the right valve the tooth is quite large 

 and extends obliquely forward and downward, and is largest at 

 its extremity ; in front of this is a depression or socket for the 

 smaller anterior tooth of the left valve, while back of it is a 

 larger cavity for the large central tooth of the left valve ; back 

 of this cavity there is a slight sharp elevation extending ob- 

 liquely backward. In the left valve there is a small, thin tooth 

 extending obliquely forward, back of which is a large socket for 

 the reception of the large tooth of the right valve. Posterior to 

 this there is a thin, deep depression, extending nearly parallel 

 to the hinge, for the reception of the thin posterior tooth of the 

 right valve. Length, 52 mm. ; height, 40 mm. ; convexity of 

 single valve, 13 mm. 



Range and distribution : Upper Coal Measures ; Kansas City, 

 Lansing ( probably from the penitentiary coal-shaft ) . 



One specimen, somewhat below the average size, was worked 

 from the shale, showing the internal and external features of 

 both valves, including the hinge. 



