BULLETIN NO. 2. 19 



faint lines of growth; lateral sides diverging for a short distance 

 below the ears, and then broadly rounding into the basal border. 



Surface ornamented with about 18 to 20 even, stout, rounded 

 ribs or costse, that are about twice as wide as the interven- 

 ing spaces. 



Length from beak to base -ff inch ; breadth 1 inch ; length of 

 hinge line about | inch. This shell may be readily distinguished 

 from others occurring in the same horizon by its broad rounded 

 costfe. 



Named in honor of my friend Prof. Orestes St. John, of Topeka, 

 Kansas. 



Position and locality : Keokuk limestone, Warsaw, 111. 



No. 2504 of the Illinois State collection. 



Collector, A. H. Worthen. 



AVICULOPECTBN NIOTENSE. (sp. nOV.) 



Shell large, orbicular, nearly or quite equilateral, length and 

 breadth about equal, hinge line shorter than the greatest width 

 of the shell. Left valve moderately convex, basal margin broadly 

 and evenly rounded, anterior ear short, triangular, and separated 

 from the lateral margin by a well-defined sinus. Posterior ear 

 more than twice as long as the anterior, and pointed at the ex- 

 tremity. Surface of the valve ornamented with numerous fine 

 radiating costae, of which about fourteen may be counted near 

 the basal margin in the space of half an inch. These costae 

 appear to become obsolete on the ears and on the lateral borders 

 of the shell. 



Length 2f inches ; breadth about the same ; length of hinge 

 line about 2 inches. 



This shell may be readily distinguished from the A. Varsoviensis, 

 described and figured in Vol. VII of these reports, by the much 

 finer radiating costae with which it is ornamented. 



Position and locality : Keokuk limestone, Niota, Hancock 

 county, 111. 



No. 2505 of the Illinois State collection. 



Collector, A. H. Worthen. 



AVICULOPECTBN ELSAHENSIS. (sp. nOV.) 



Shell of medium size, left valve moderately convex, and exclu- 

 sive of the ears presenting a slightly oblique sub-trigonal outline; 

 hinge line equaling about two-thirds the greatest width of the valve ; 

 basal outline forming a somewhat oblique semi-circular curve ; 

 posterior margin straight from the base of the ear to the basal 

 curve where the valve attains its greatest width. Anterior margin 

 regularly rounded ; anterior ear small and obtusely angular ; pos- 

 terior ear large, triangular, and sharply pointed at the extremity. 

 Surface of the ears apparently without ornamentation. Surface 

 of the shell ornamented with numerous radiating costae that in- 



