PALEONTOLOGY OF IOWA. 705 



This differs from the specimen fig. 3 a, not only in size, but also in the fewer costae 

 and more distinctly punctate surface, with the lines of growth scarcely visible. For 

 the preseut, I propose to recognize this as a distinct variety. 



Fig. 3 b. View of the dorsal valve, showing the beak and broken foramen of the oppo- 

 site valve. 

 Fig. 3 c. Yentral valve of the same specimen. 



Geological formation and locality. In the Kaskaskia limestone t Chester, 

 Illinois. 



Spirifer setigerus ( n. s .). 



PLATE XXVII. FIG. 4 a, b. 



SHELL depressed orbicular, gibbous on the umbones : car- 

 dinal line shorter than the width of the shell below. Dorsal 

 valve broadly elliptical, elevated in the middle by an un- 

 defined mesial sinus, prominent on the lower half of the 

 shell, becoming obsolete before reaching the beak ; beak in- 

 curved, with a broad foramen below and distinctly denned 

 area, which is sharply limited by the exterior shell. Ventral 

 valve a little more convex on the umbones than the dorsal 

 valve : mesial sinus reaching to the beak in a narrow de- 

 pression, which becomes deeply marked below the middle of 

 the shell ; umbo prominent, rounded, with the beak curving 

 over the foramen ; area high, short, contracted by the en- 

 croachment of the exterior shell which curves inwards along 

 the margins, vertically striated : foramen large, wider at 

 base than the length of the side. 



SURFACE marked by fine concentric and radiating strias ; 

 the concentric striae becoming at intervals lamellose, and the 

 margin extended into numerous setiform spines, the bases 

 of which usually remain upon the surface of well preserved 

 specimens. 



This species is more rotund than that of the Keokuk limestone; the area is much 

 shorter, and the mesial fold and sinus more strongly defined. From Spirifer lineatus, 

 it differs in its less rotundity and the more strongly defined mesial fold and sinus. 



Fig. 4 a. View of the dorsal valve, showing the beak of the opposite valve. 

 Fig. 4 b. Ventral valve of the same specimen. 



Geological position and localities. In the Kaskaskia limestone : Kaskaskia 

 and Chester, Illinois. 



[ IOWA SURVEY.] 89 



