[OTERTEBRATE8. 109 



SCHIZODUS DEPRESS!-*. Worthen. 



PI. XVIII, Fig*. S-a. 



Schizodus depresses, Worthen, March. 18&4. Bulletin No. 2. of the Illinois State Museum 

 of Natural History, page II. 



Shell below the medium size, transversely ovate, .slightly con- 

 vex, beak depressed, posterior extremity cuneate, anterior ex- 

 tremity regularly rounded into the semi-ovate curve of the basal 

 region. Posterior side a little longer than the anterior, and 

 rather sharply rounded at the extremity : dorsal margin rapidly 

 sloping towards the anterior extremity; surface smooth. 



Length of an average size specimen 9 / 16 inch; height from 

 beak to basal margin " li; inch: convexity of the valves about 

 % inch. 



This species may be readily distinguished from all previously 

 described species by its generally depressed form. 



Position and locality: Oolitic beds of the St. Louis group, 

 Monroe county, 111. 



Collector, A. H. Worthen. 



No. 2520 of the Illinois State Museum. 



Si Hizoors? ciRruLrs. Wort hen. 



PI. XIX. Fig. 1. 



circulus. Worthen. March, 1884. Bulletin No. 2, of the Illinois State Museum 

 of Natural History, page 11. 



Ill the collection from the oolitic beds of Monroe county, there 

 are three or four detached valves of a small shell, that are doubt- 

 fully referred to the genus Scbizodus, and which may be charac- 

 terized as follows: 



Shell small, nearly circular in outline, slightly inequilateral, 

 valves slightly convex, beaks depressed, and extending slightly 

 beyond the cardinal border. A very slight umbonal ridge is 

 apparent on some of the specimens that becomes obsolete before 

 reaching the basal margin. Surface smooth. Height from beak 

 to base "/, inch: length % inch. 



This shell resembles the form figured and described by Prof. 

 M'-i'uy in his "Synopsis of the Garb. Fossils of Ireland," PI. XI, 

 fig. 13, but is much more nearly circular than his Dolabra orbi- 

 cnlaris. 



