134 PALEONTOLOGY OF ILLINOIS. 



PTEROPODA. 



GENUS CONULARIA. Miller. 

 CONULARIA CHESTER KXKIS. Worthen. 



PL XI, Fig. <Ma. 

 Conularia chesterensis Worthen, 1883. Geol. Surv. of Illinois, Vol. VII, page 325. 



Shell attaining a medium size, long and rather slender, grad- 

 ually tapering, nearly equally four-sided, the four angles being 

 distinctly and rather deeply furrowed, while a slight furrow 

 marks the median line on each side. The sides are crossed by 

 numerous raised costae, which arch slightly forward from the 

 angles to the median line, making an angle with that line of 

 about 14. These costae do not cross the angular furrows, but 

 are alternately arranged so that those on one side terminate 

 at the intervening space between those on the opposite side. 



These spaces are about twice as wide as the costae, and are 

 widest at the median line. 



The aperture is not well preserved in any of our specimens, 

 but the shell was evidently notched at the angles, and was pro- 

 bably contracted at ttie aperture. 



Length of a rather large individual, 5 inches; breadth between 

 the angles near the aperture, 1 inch; number of costae in the 

 space of an inch near the aperture, 20: near the apex, 30. 



Position and locality: Chester limestone, Chester, Illinois. 



Collector A. H. Worthen. 



No. 2489 of the Illinois State Museum. 



