PLATE X— Continued. 



DeRBYA ROBU8TA, Hall. 



Fig-. 12. The extenor of a compressed brachial valve, in which the lailial striae of the shell are strongly 

 developed. 



Pig-. 13. An enlarg-ement of the cardinal process from another specimen. 



Figs. 14 1 17 in error], 15. Pi-otile and brachial views of a large individual ; showing- the external charac- 

 ters of the species. 



Fig-. 16. 'I'he intenor of the cardinal portion of the pedicle-valve ; showing- the character of the musculai- 

 scars, the strong but short median septum, projecting teeth and the convex deltidium. The 

 projecting tooth on the i-ig-ht-hand side of the figure has become double from abnoi-mal growth. 



Fig-. 17. The exterior of a petlicle-valve ; showing Ihe character of the striae, which differ in some degree 

 from their uniformity shown in the specimen represented in figs. 14 and 15. 

 Coal Measures. St. Clair county, Illinois. 

 For other illustrations, see Paleontology of Eastern Nebraska, plates v and viii. 



Genus MEEKELLA, White and St. John. 



Page 264. 



Meekella striatocostata, Cox. 



Fig:. 18. Profile of a specimen i-etaining 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, nai-row deltidium, and the bases of 



the crui-al 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 which the apex of the pe<licle-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 portion of the process is incorrectly represented as having three instead 



of two lobes. 

 Fig. 23. A longitudinal section of the specimen represented in fig. 19 ; sho-wing the extent of the dental 



lamellse and crural plates, to the latter of which one of the crura is attached. 

 Coal Measures. Near Wint&set, Iowa. 

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



pp. 120, 121 ; and Paleontology of Eastern Nebraska, plate v. 



