PALAEONTOLOGY OF IOWA. 509 



Gco^gical formation and localities. In calcareous shale of the age of the 

 Hamilton group : Independence ( Iowa) ; Rock-island ? ( Illinois). 



Spirifer parryaims ( n. s.). 



PLATE IV. FIG. 8 a, b. 



SHELL subglobose, transversely subelliptical ; cardinal ex- 

 tremities usually rounded ; valves almost equally convex. 

 Ventral valve gibbous in the middle and on the umbo ; beak 

 slightly incurved ; mesial sinus well defined from the beak 

 and broadly expanded below, with the margins less strongly 

 defined, curvilinear within : area high, extending to the 

 hinge extremities, and limited by a sharp angle above ; 

 foramen large, and open to the apex of the shell. Ventral 

 valve very gibbous in the middle, strongly arcuate towards 

 the baso-lateral margins, and abruptly curved at the umbo ; 

 mesial sinus prominent, rounded, much elevated and deeply 

 emarginate in front for the reception of the projecting mesial 

 extension of the opposite valve. 



SURFACE marked by about seventeen, eighteen or more 

 simple broadly rounded and little elevated plications on 

 each side of the mesial fold and sinus, which are separated 

 from each other by very narrow shallow grooves. In perfect 

 specimens, the entire surface of plications and mesial fold 

 and sinus are covered by extremely minute radiating strise, 

 and crossed by equally fine concentric striae and a few im- 

 bricating lines of growth. 



This species bears considerable resemblance to the S. granulifera of the Hamilton 

 group of New- York, but it is a smaller shell, the mesial fold is not depressed in the 

 centre, and there is no elevation in the sinus as in that species; while in well pre- 

 served specimens, the granulose surface of the one, and the finely striated surface of 

 the other, contrast sufficiently to afford a ready means of distinction. 



The S. granulifera is not known in the Mississippi valley up to this time. The S. 

 eatoni and S. clintoni of the Hamilton group of New- York resemble this shell in 

 some respects. 



Fig. 8 a. Dorsal view, showing the beak of the ventral valve, the area in part, with the 



foramen projecting beyond the hinge line of the dorsal valve. 

 Fig. 8 b. Ventral valve of the same specimen. 



Geological formation and locality. In calcareous shale of the age of the 

 Hamilton group of New-York : New-Buffalo, Iowa. 



