16 BULLETIN NO. 2. 



GENUS MODIOLA, Lamark. 



MODIOLA ILLINOIENSIS. (sp. nOV.) 



Shell below medium size, length from the anterior to the pos- 

 terior extremities a little more than twice the width of the valves, 

 narrowing rather rapidly behind the posterior extremity of the 

 hinge line ; valves strongly convex in the umbonal region, and 

 obliquely across the valve to the ventral margin, compressed be- 

 hind ; beaks depressed, hinge line equal to three-fifths the entire length. 

 A shallow depression extends from the beak obliquely to the ventral 

 margin in front of the umbonal ridge, posterior margin narrowly 

 rounded, anterior extremity obtusely pointed, ventral margin slightly 

 sinuate in the middle, hinge line straight, surface nearly smooth 

 but showing a few obscure lines of growth. 



Length of an average size specimen 1| inch ; breadth at the 

 posterior extremity of the hinge line fg- inch ; convexity of the 

 valve about y^ inch. 



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

 group, Monroe county. 111. 



No. 2518 of the Illinois State collection. 



Collector, A. H. Worthen. 



GENUS CAEDIOMORPHA, DeKoninck. 



CARDIOMOKPHA ? PELLAENSIS. (sp. nOV.) 



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

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

 gin 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 sur- 

 face ornamentation. 



Length f^ inch; height ^V inch; thickness f^ inch. 



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

 Pella, Iowa. 



No. 2516 of the Illinois State collection. 



Collector, A. H. Worthen. 



GENUS PLEUROPHOEUS, King. 



PLEUROPHORUS CHESTERENSIS. (sp. nOV.) 



Shell of medium size, nearly cylindrical when the valves are 

 closed, almost three times as long as high, most strongly convex 



