660 GEOLOGICAL SURVEY OF IOWA. 



Fig. 4 a, b. Dorsal and ventral views of a specimen of the ordinary form. 

 Fig. 4 c. Profile of the same. 



Fig. 5. Dorsal view of a broader form, showing a wide mesial lobe, with a narrow 

 impression down the centre. 



Geological position and localities. In limestone of the age of the Warsaw 

 limestone : Bloomington and Spergen hill, Indiana. 



Spirifer subcardiiformis ( n. s.). 



PLATE XXIII. FIG. 6 a, b. 



SHELL somewhat depressed globose, gibbous towards the 

 beaks and depressed towards the basal and lateral margins : 

 valves subequal. Dorsal valve a little the less convex : beak 

 rising above the hinge-line, with a comparatively large tri- 

 angular area beneath : mesial fold little elevated, marked 

 in the middle and at base by four strong plications which 

 originate at the beak as a single one ; about seven simple, 

 strong, rounded and little elevated plications on each side. 

 Ventral valve with the beak a little elevated above the 

 opposite, incurved : mesial sinus faintly denned and marked 

 by three strong plications, one of which lies in the centre 

 and one on each side, with seven or eight on the lateral por- 

 tions of the shell : area short and high, little extended on 

 each side of the large foramen, which forms nearly an equi- 

 lateral triangle. 



The surface marking appears to have been minutely 

 striato-punctate, but it is not well preserved in the only 

 specimen examined. 



The only European Carboniferous species that resembles this, is the 5. rotundatus; 

 from which this species is distinguished by its short high area, its larger foramen, 

 its more equal beaks, and less number of plications. 

 Fig. 6 a. Ventral valve, the specimen a little distorted from pressure. 

 Fig. 6 b. Dorsal view of the same, showing the area and foramen of the opposite valve. 



Geological formation and locality. In the Warsaw limestone, above 

 Alton, Illinois. 



