110 PALAEONTOLOGY OF ILLINOIS. 



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

 Monroe county, 111. 

 Collector, A. H. Worthen. 

 No. 2521 of the Illinois State Museum. 



SCHIZODUS ULRICHI. (sp. 11OV.) 

 PL XXI. Figs. 1-la. Ib. PL XX. Fig. 9. 



Shell above a medium size, ovate, valves moderately com- 

 pressed; beaks strongly incurved forward, and situated a little 

 less than one-half the length of the shell from the anterior mar- 

 gin. Anterior border evenly rounded up from the basal margin 

 to the beaks. Hinge line short ; basal margin rather long, and 

 gently curving behind to the rather narrow posterior extrem- 

 ity. Lunule clearly denned, but not deep. A slightly elevated 

 umbonal ridge extends from the beaks to the posterior extrem- 

 ity. Surface smooth except some faint lines of growth near 

 the basal margin. 



Anterior adductor muscular scar nearly circular, and situated 

 about half way from the beak to the base of the anterior mar- 

 gin; posterior muscular scar not so well defined, and situated 

 about equi-distant from the beaks to the posterior extremity. 



Length of a specimen of average size, l 9 /ie inches; breadth 

 from the beaks to the cardinal border 1% inches ; thickness with 

 the valves united 1 inch. 



This shell has been confounded with S. wheeleri, Swallow sp. 

 but differs from that shell as usually figured in its larger size, 

 depressed umbonal slopes and ovate outline. 



Position and locality : Upper Coal Measures, Fairfield, Wayne 

 county, Illinois. 



No. 2584 of the Illinois State Museum. 



SCHIZODUS RANDOLPHENSIS. (sp. nOV.) 

 PL XX, Fig. 12. 



Shell elongate ovate, truncated at the anterior extremity and 

 narrowly rounded behind. Beak depressed, projecting beyond 

 the hinge line, and situated close to the anterior extremity. 



