BULLETIN NO. 2. 11 



Length from the beak to the ventral margin measuring obliquely, 

 2 inches ; greatest breadth If inches. 



Position and locality : Keokuk limestone, Nauvoo 111. 

 No. 2499 of the Illinois 8tate collection. 

 Collector, A. H. Worthen. 



SCHIZODUS DEPRESSUS. (sp. UOV.) 



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

 vex, beak depressed, posterior extremity cuneate, anterior extremity 

 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 j% inch ; height from beak 

 to basal margin y^ 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. 



No. 2520 of the Illinois State collection. 



Collector, A. H. Worthen. 



SCHIZODUS? CIRCULUS. (sp. UOV.) 



In 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 ScJuzodus, and which may be character- 

 ized 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 Vg- inch ; length ^ inch. 



This shell resembles the form figured and described by Prof. 

 McCoy in his "Synopsis of the Carb. Fossils of Ireland," PI. XI, 

 fig. 13, but is much more nearly circular than his Dolahra orbicu- 

 laris. 



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

 Monroe county. 111. 



No. 2521 of the Illinois State collection. 



Collector, A. H. Worthen. 



GENUS ALLORISMA, King. 



ALLORISMA ILLINOIENSIS. (sp. UOV.) 



Shell large, elongate-ovate, length a little more than twice the 

 height ; valves moderately convex, extremities broadly rounded ; 

 dorsal margin straight and nearly parallel with the base ; anterior 



