PLATE X— Contiuueii. 



Derbya robusta, Hall. 



Fig-. 12. Thf exterior of a compressed brachial valve, in whicli the radial strife of the shell are .^itrongly 



developed. 

 Fig. 13. An enlargement of the cardinal process from another specimen. 

 Figs. 14 (17 in eri'or], 15. Profile and brachial views of a large individual ; showing the external ch.arac- 



tei's of the species. 

 Fig. 16. The interioi- of the cardinal portion of the pedicle-valve ; showing the character of the muscular 



scai-s, the strong but short median septum, projecting teeth and the convex deltiilium. The 



projecting tooth on the right-hand side of the figure has Tiecome double fiom abnormal growth. 

 Fig. 17. The exteiior of a peilicle-valve ; .showing the chai'acter of the striae, which differ in some degree 



fi'om their uniformity .shown in the specimen represented in tigs. 14 .and 15. 

 Coal Measures. St. Clair county, lUiJiois. 

 For other illustrations, see Palseontology of Eastern Nebi-aska, plates v and viii. 



Genus MEEKELLA, White and St. John. 



Pag-e 26t. 



Meekella striatocostata, Cox. 



Fig. IS. Protile of a specimen retaining both valves; showing the great elevation of the cardinal area of 



the pedicle-valve. 

 Fig. 19. Cardinal view of a Larger individual ; showing the high area, narrow deltidinm. and the bases of 



the ci'ural plates in the brachial valve. 

 Fig. 20. A view of the pedicle-valve of the same sjiecimen. 

 Fig. 21. A cardinal view of a specimen from whii'h the apex of the peilicle-valve has been removed to 



show the dental lamellse. 

 Fig. 22. An enlargement of the cardinal process ; showing the extreme elevation of the lobes and the cru- 

 ral plates. The central iiortion of the process is incorrectly represented as having three instead 



of two lobes. 

 Fig. 23. A longitudinal section of the specimen i-epresented in fig. 19 ; showing the extent of the dental 



lamellae and crural plates, to the latter of which one of the ci-ura is attached. 

 Coal Measures. Near Whiterset. Iowa. 

 For other illustrations, see Transactions of the Chicago Academy of Nafnral Sciences. Volume I, 



PI1. 120, 121 ; and Palseontology of Eastern Neljraska, jilate v. 



