PLATE X. 



Paeastrophia Greenii, Hall. 



Page 364. . 



Figs. 1-4. Ventral, profile, dorsal and cardinal views of an internal cast; show- 

 ing the character of the plication of the surface and the median septum 

 of each valve. 



Fig. 5. Cardinal view of another individual; showing the cavities left by the 

 median septa. 

 Niagara dolomites. Near Milwaukee, Wisconsin. 



Parastrophia latiplicata, Hall. 



Page 365. 



Fig. 6. An internal cast of a brachial valve; showing the few broad plications 

 and the extent of the median septum. 



Fig. 7. An internal cast of the brachial valve in which the filling of the 

 spondylium is exposed and the four scars of the adductor impression dis- 

 tinctly retained. 



Figs. 8, 9. Profile and cardinal views of the same specimen. 



Fig. 10. Anterior view showing the elevation of the median fold and char- 

 acter of the plication. 

 Niagara dolomites. Near Milwaukee, Wisconsin. 



Parastrophia divergbns, Hall. 

 Page 364. 



Figs. 11, 12. Ventral and dorsal views showing the spondylium and septa in 



the umbonal region. 

 Fig. 13. Cardinal view of a specimen which has been transversely sectioned in 



the umbonal region, the brachial valve being represented above; showing 



the spondylia. x 1^. 

 Fig. 14. Anterior view of the specimen represented in figs. 11, 13. 

 Hudson River group. Wilmington, Illiaois. 



Parastrophia multiplicata, Hall. 

 Page 365. 



Figs. 15, 16. Anterior and profile views of an internal cast; showing the 

 broad, strong plications, of which there are four on the fold and three in 

 the sinus. 

 Fig. 17. Cardinal view of another and rather more convex internal cast; show- 

 ing the cavities left by the median septa. 

 Niagara dolomites. Near Milwaukee, Wisconsin. 



394 



