PLATE XI. 



(Figures 1-32 by R, P. Whitfield.) 



Legend. D. Deltidiiim, pedicle- valve. a. Median septum. 



C. Deltidium, brachial valve. j. Cardinal process, 



t. Teeth. i-. Diductor scai-s. 



d. Dental lamellaE. a. Anterior adductors. 



b. Dental sockets. a'. Posterior adductors. 



c. Ci'ural plates. 



Genus DERBYA, Waagen. 



Page 2(il. 



Derbya Keokuk, Hall. 



Figs. 1, 2. An internal cast and gutta-percha impression of the central cardinal area, viewed fi-om the bra- 

 chial valve ; showing the character and extent of the muscular area, cardinal process, dental 

 lamellae and median septum. 



Keokuk beds (Knobstone group). New Providence, Indiana. 

 Fig. 3. An partial cast of the interior of a pedicle-valve ; showing the muscular scars and impi'ession of 

 the median septum. 



Keokuk beds. Keokuk, Iowa. 



DeEBYA (?) BILOBA, Hall.* 



Fig. 4. A cardinal view ; showing the ventricose brachial valve and short area of the pedicle-valve. X 2. 

 Fig. 5. A view of the brachial valve ; showing the bilobed contour of the shell, obdurate outline, the short 

 cardinal area and deltidium of the opposite valve. X 2. 

 Coal Measures. Wintei'set, Iowa. 



STREPTORHYNCHUS, King. 



Page 267. 



yTEEPTORHY'NCHUS Hallianus, Derby. 



A view from the brachial valve of an entire shell. 



A posterior view of the cardinal process ; showing the lobation of the postei'ior face, the elevated 

 crural plates and the grooved deltidium. X 2. 



An enlarged view of the same parts, from above ; showing also the character of the adductor im- 



pi-essions. X 2. 

 The cardinal pi'ocess of a larger individual ; showing the grooving of the extremities of the lobes. 

 A profile of the same ; showing the backward extension of the process and the great elevation of 



the crural plates. X 2. 

 A posterior view of the same. X 2. 



The cardinal process of another specimen ; showing a greater elevation and deeper bifurcation. 

 The exterior of an unsymmetrieal pedicle-valve ; slightly restored about the left ante-lateral 



margin, and showing the strongly alternating striae. 

 The interior of the same valve ; showing the unsuppoi'ted teeth, and the character of the muscu- 

 lar scars. 

 The exterior of a pedicle- valve, having a plicated exterior similar to that of Meekella and Strep- 



tm-hynchus pectiniforinis,'Da,\\(\son. The shell is unsymmetrieal and the outline is partially 



restored. 

 The interioi- of the same specimen ; showing the cardinal area, closed delthyrium, the projecting 



teeth, and the flabellate muscular impression. 

 A view looking into the umbonal cavity of the specimen repi-esented in fig. 14 ; showing the 



absence of dental lamellae and median septum. 



Upper Carboniferous. Bomjardim and Itaituba, Prcuince of Para, Brazil. 



Fig. 



6. 



Pig. 



7. 



Fig. 



8. 



Fig. 



9. 



Fig. 



10. 



Fig. 



11. 



Fig. 



12. 



Fig. 



13. 



Fig. 



14. 



Fig. 



15. 



Fig. 



16. 



Fig. 



17. 



* Report of the New York State Geologist for 1882 (pub. 18S3), explanation of plate (xi) 41, figs. 4 and 5. 



