71 



Kansas, aud not uncommon at Kansas City, Missouri. In D. 

 convexa there is a shallow depression directly under the beak, 

 on the posterior side, which is not manifest in this species. In 

 D. convexa the beak is more obtuse, less incurved, and situated 

 nearer the posterior margin, than it is in this species. The 

 radiating lines that ornament the dorsal valve in this species 

 have not been noticed in D. convexa, beside this species seems 

 to be the smaller of the two. 



DISCINA MUNDA, n. sp. 



Plate VI, Fig. 6, dorsal view; Fig: 7, lateral view of the same 



valve. 



Shell medium size, elhptical, height less than one-third the 

 length. Dorsal valve most convex anterior to the beak and 

 near the posterior third of the shell, from which part it slopes 

 regularly to the lateral and anterior margins. Beak acute and 

 situated almost directly above the posterior margin of the 

 shell. The shell is concave from the point of the beak to the 

 posterior margin. 



Surface jet black and marked by fine concentric lines only 

 just visible to the unaided eye. 



We know of no species with which it is necessary to com- 

 pare this one. 



Found in the Upper Coal Measures at Kansas City, Missouri, 

 and now in the collection of Wm. F. E. Gurley. 



