126 PALEONTOLOGY OF ILLINOIS. 



Length of an average size specimen ir> /i inch; breadth at the 

 posterior extremity of the hinge line 7 /i inch; convexity of the 

 valve about 3 / 1( , inch. 



Position and locality : From the oolitic beds of the St. Louis 

 group, Monroe county, 111. 



Collector, A. H. Worthen. 



No. 2518 of the Illinois State Museum. 



GENUS CARDIOMORPHA, DeKoninck. 

 CARDIOMORPHA? PELLENSIS. Worthen. 



PI. XIX, Figs. 9-9a, 9b. 



Cardiomorpha pellaensis, Worthen, March, 1884. Bulletin No. 2 of the Illinois State 

 Museum of Natural History, page Hi. 



Shell longitudinally sub-ovate, length less than once and a 

 half the height; dorsal and ventral borders sub-parallel, dorsal 

 margin nearly straight, ventral margin moderately curved ; 

 valves convex, the greatest convexity being about one-third the 

 distance from the beaks to the ventral margin ; beaks depressed 

 and placed close to the anterior extremity which is nearly straight 

 above, and curving below into the ventral margin; posterior 

 extremity cuneate. 



The specimen is a cast in a calcareous shale, and shows no 

 surface ornamentation. 



Length 11 / le inch; height 7 /i inch; thickness 5 / 16 inch. 



Position and locality : Shaly limestone of the St. Louis group, 

 Pella, Iowa. 



Collector, A. H. Worthen. 



No. 2516 of the Illinois State Museum. 



GENUS BAKEVELLIA, King. 

 BAKEVELLIA ILLINOIENSIS. Worthen. 



PI. XVIII, Fig. 4-4a. 



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

 of Natural History, page 14. 



Shell about medium size, elongate sub-rhomboidal, left valve 

 moderately convex from a ridge which extends from the beak 

 about two-thirds the distance to the cardinal border where it 

 becomes obsolete. 



