INVERTEBRATES. 121 



This genus has not hitherto been recognized so far as known 

 to the writer in strata below the Coal Measures in this country, 

 but in Europe it has been found in Lower Carboniferous strata, 

 and two specjes have been described and figured by Prof. L. G. 

 de Kouiuck from the Carboniferous limestones of Belgium. 



Description: Shell of medium si/e. ovate, umbones depress* 1 . 

 valves moderately convex, the greatest convexity being some- 

 what nearer the hinge line than the basal margin. Hinge line 

 straight, and about two-thirds as long as the antero-posterior 

 diameter of the valves. Posterior side shorter than the anterior 

 and gradually rounded from the hinge line to the basal margin. 



Surface ornamented with 28 to 30 rounded striie. each alter- 

 nate one being smaller than the others, and extending only 

 about half way to the hinge line. 



Height 1:j ]f . inch: breadth % inch; length of hinge line 7 /i 6 

 inch. 



Position and locality: Chester shale, Chester, 111. 

 Collector. A. H. Worthen. 

 No. 2593 of the Illinois State Museum. 



GENUS EDMONDIA, DeKoninck. 

 EDMONDIA VARSOVIKNSIS. Worthen. 



PL XX, Figs. 11-lla. 



Edmondia varsovienses, Worthen, March, 18&4. Bulletin No. 2 of the Illinois State 



of Natural History, page 18. 



Shell above the medium size, compressed ,-uid evenly rounded 

 at the extremities; length about one-third greater than the 

 height: basal margin broadly semi-ovate in outline, dorsal mar- 

 gin sloping abruptly from the beaks in front, and nearly straight 

 behind for about two-thirds the entire length of the shell, and 

 thence rounding into the posterior margin: beaks depressed and 

 located near the anterior extremity. 



The surface of the cast shows traces of delicate closely ar- 

 ranged concentric stria*, and a few more distinct lines of growth. 



Length of the typical specimen 2' s inches: height 1% inches. 

 This shell is only known from limestone cae 

 15 



