510 PALEONTOLOGY OF ILLINOIS. 



ally in the genus Lithopliaga, from the similarity of the external charac- 

 ters to some of the recent species of that genus. 



Locality and position Warsaw, Illinois; Warsaw division of the 

 Lower Carboniferous series. 



GENUS 

 MYALINA ST. LUDOVICI, Worthen Ms. 



PI. 22, Fig. 3. 



SHELL below the medium size, snb-qnadrate, oblique; 

 length about once and a half the width; hinge straight, 

 and equaling the greatest width of the shell below ; basal 

 margin regularly rounded; beak of the left valve pointed, 

 and curving obliquely forward. Surface marked by regu- 

 lar concentric lamina from the beak to the basal margin, 

 the distance between them gradually increasing from the 

 beak downward. 



This species may be readily distinguished from any other known to 

 us in the Lower Carboniferous Limestones, by the strong concentric 

 laminae upon its surface. 



Position and locality St. Louis Limestone; Alton, Illinois, and St. 

 Louis, Missouri. 



GENUS CH^tfOMYA, M. and H. 



CELENOMYA 1 ? KHOMBOIDEA, M. and W. 



PI. 22, Fig. 4. 

 Chcenomya 1 rhomboidea, MEEK and WORTHEN, 1865. Proceed. Acad. Nat. Sci., Phila., p. 250. 



SHELL rather small, short, moderately convex; outline 

 rhombic, as seen in a side view; basal and dorsal margins 

 nearly straight and parallel, the former very abruptly curv- 

 ed upwards behind, and more gradually in front; anterior 

 side very short and truncated, or a little rounded; poste- 

 rior side distinctly truncated (obliquely) nearly the entire 

 breadth or hight of the valves, gaping but not dilated; 



