PLA.TE VI. 

 Dbrbya cymbula, Hall. 

 Page 348. 

 Figs. 1, 2. Dorsal and cardinal views of a large specimen. 

 Upper Coal Measures. Near Kansas City, Missouri. 



Stbeptorhynchus Ulkichi, Hall. 

 Page 350. 

 Fig. 3. The interior of a pedicle-valve referred to this genus on account of 

 the peculiar form of the shell and the absence of a median septum. 

 Chester limestone. Crittenden county , Kentucky . 



Orthotkopia DOLOMiricA, Hall. 



Page 343. 



Fig . 4 . Ventral view of an internal cast ; showing the form of the shell, the 

 short straight hinge and the conspicuous muscular scars. 



Fig. 5. The interior of a pedicle- valve, showjng the cardinal area, open 

 delthyrium, muscular scar and short median septum. 



Figs, t), 7, 8. Dorsal, ventral and cardinal views of an internal cast, showing 

 the form of the muscular impressions, the median septum in each valve 

 and the elevation of the cardinal area, x 2. 

 Niagara dolomites. Near Milwaukee, Wisconsin. 



SrROPHONBLLA COSTATULA, Hall. 



Page 354. 



Figs. 9, 10. Dorsal and profile views of the shell, showing the reversed con- 

 vexity of the valves and the sharp, irregularly dichatomizing plications. 

 Niagara group. Louisville, Kentucky. 



PliECTAMBONITES PRODUCTA, Hall. 



Page 354. 



Figs. 11, 12. Profile and front views of an internal cast of a pedicle-valve. 

 Niagara dolomites. Yellow Springs, Ohio. 



CflRISTIANIA SUBQUADRATA, Hall. 



Page 351. 

 Figs. 13, 14. Two views of a pedicle- valve, showing its elongate form, smooth 



or squamous surface. 

 Fig. 15 . The interior of a pedicle- valve, with an open delthyrium and showing 



the muscular walls and scars. 



Fig. 16. The exterior of a brachial valve, showing the cardinal process and 

 edges of the crural plates. 



384 * . 



