INVERTEBRATES, 107 



LAMELLIBRANCHIATA. 



GENUS LEPTODOMUS. McCoy. 

 LEPTODOMIS? MAI;. NTS. Worthen. 



PI. XYIII, Fig. 2. 



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



Natural History, page 9. 



Shell large, ovate sub-quadrangular, convex, the greatest con- 

 vexity being about half-way from the beaks to the ventral mar- 

 gin; anterior extremity comparatively long and broadly rounded, 

 posterior side about once and a half the length of the anterior, 

 obliquely flattened behind the beaks with a well defined umbonal 

 ridge extending diagonally from the beak to the posterior ex- 

 tremity of the ventral margin. Dorsal margin straight from 

 the beaks to the obliquely truncated posterior margin. 



Beaks long, strongly recurved, and projecting about % of an 

 inch beyond the dorsal margin. 



Length 7 /i 6 inches; height 2% 6 inches; convexity of the valve 

 about % inch. 



This is from one of the upper divisions of the Chester lime- 

 stone, about two miles below the mouth of Mary's river, Ran- 

 dolph county; 111. 



Collector, A. H. Worthen. 



No. 2498 of the Illinois State Museum. 



GENUS SCHIZODUS. King. 

 SCHIZODUS VARSOVIENSIS. Worthen. 



PL XIX, Fig. 7. 



Schizodus varsoviensis, Worthen, March, 1884. Bulletin No. 2, of the Illinois State 

 Museum of Natural History, page 10. 



Shell of medium size, transversely ovate, moderately convex 

 in the anterior and umbonal regions, cuneate posteriorly ; anter- 



