PALEONTOLOGY OF IOWA. 663 



Spirifer subequalis ( n. s.). 



PLATE XXIII. FIG. 9 a, b, c. 



SHELL semielliptical, about twice as wide as long : valves 

 almost entirely equal, the beak of the ventral valve being 

 very slightly elevated above the opposite. Dorsal valve 

 depressed convex ; the mesial fold obtusely angular, scarcely 

 defined at its margins : a narrow cardinal area, which is 

 conspicuous in well preserved specimens. Ventral valve 

 somewhat gibbous on the umbo : beak slightly incurved : 

 mesial sinus not observable on the upper half of the shell, and 

 becoming a broad depression with undefined margins below : 

 area of moderate width, extending to the cardinal extremi- 

 ties ; foramen large, the width at base greater than the 

 length of the side. 



Entire surface, including sinus and fold, marked by sim- 

 ple rounded plications, which bifurcate near the beak, and 

 of which there are about eighteen on each side, and about 

 eight on the mesial fold and ten in the sinus ; concentrically 

 marked by undulating laminae of growth and finer stride. 



Fig. 9 a. View of the ventral valve. 



Fig. 9 b. Dorsal view, showing the beak of the opposite valve rising a little above the 

 other. 



Fig. 9 c. Cardinal view, showing the area and foramen. 



Geological formation and locality. In the Warsaw limestone : Warsaw, 

 Illinois. 



Cypricardella nucleata. 



PLATE XXIII. FIG. 10 a, b, c, d. 

 Cypricardella nucleata : HALL, Transactions of the Albany Institute, Vol. iv, 1856. 



SHELL inequilateral, sub quadrangular, gibbous ; anterior 

 end short, rounded ; posterior end broader, abruptly com- 

 pressed, vertically truncated at the extremity : beak nearer 

 the anterior end, small. Posterior umbonial slope extremely 

 gibbous (a broad undefined ridge), reaching to the base of the 

 truncation. 



