PLATE VII. 



(Figures 1-24, 29-3-2 by R. P. Whitfield; 33-35 by F. B. Meek; 25-28 oopiea.) 



Legend. A. Cardinal area. 



DA. Cardin?! area, brachial valve. 

 VA. Cardinal area, pedicle-valve. 

 F. Foramen. 



D. Deltidium. pedicle-valve. 

 i\. Delthyrium, pedicle-valve. 

 C. Deltidium, brachial valve, 

 t- Teeth. 



d. Deatal lamellfe. 

 b. Dental sockets. 



j. Cardinal process, 



c. Crura. 



s. Septum. 



X. Umbonal vault, 



y. Cast of umbonal vault, 



p. Pedicle muscular scar, 



a. Anterior adductors, 



a'. Posterior adductors. 



r. Diductors. 



liHIPIDOMELLA, GEhleet. 



Page 208. 

 (See Plates VI, VIa.) 



Orthis Pecosi, Marcou. 

 Fig-. 1. An entire specimen viewed from the brachial valve. X 2. 

 Fig. 2. Profile of the same. X 2. 



Fig. 3. The interior of the pedicle-valve ; showing the narrow cardinal area and the characteristic mus- 



culai- seal's. X 2. 

 Fig. 4. An enlargement of the surface ; showing the openings of the oblique tubules and minute punctse. 

 Coal Measures. Near Springfield, Illinois. 



Orthis Penniana, Derby. 



Fig. 5. View from the pedicle-valve. 



Fig. 6. Pi-ofile of the same specimen. 



Fig. 7. The interior of the pedicle-valve^; showing the nearly obsolete cardinal area and the strong mus- 

 cular impressions, especially that of the pedicle-scar. 



Fig. S. The interior of an imperfect bi-achial valve ; showing the cardinal process, crural bases and mus- 



culai' impressions. 

 Fig. 9. The cardinal portion of the same specimen, enlarged to show the low, thick cardinal process, the 



veiy prominent crura and the quadripartite character of the adductor area. X 3. 

 Fig. 10. An enlargement of the extern.al surface ; showing strong punctation. 

 Coal Measures. Itaituba, Brazil. 



ORTHOTICHIA, nom. propos. 



Page 213. 



Orthis (?) Mokganiana, Derby. 



Figs. 11, 12. Interiors of imperfect brachial valves ; showing the cardinal process, the greatly elevated and 

 curved ci-ura supported by septal plates which are pi-oduced about the sides of the muscular 

 area. In fig. 12 are also seen the accessory adductor scars described by Dr. Derby. 



Fig. 13. Section in profile of fig. 12 ; showing the extent of the crural plates and the elevation of the crura. 



Fig. 14. The interior of a pedicle-valve, retaining the long dental lamellae and the median septum. 



Fig. 15. A slightly oblique view of another interior of this valve ; showing more distinctly the elevation of 

 the teeth and the outline of the muscular area. 

 Coal Measures. Itaituba, Brazil. 



Fig. 



16 



Fig. 



17. 



Fig. 



18. 



Fig. 



19. 



Genus BILLINGSELLA, gen. nov. 



Page 230. 



(See Pliite VIIa, figs. 7-9.) 



BiLLINGSELLA PePINA, Hall. 



The extei'ior of a brachial valve ; drawn from a gutta-percha impression of a natui-al mould. 

 A natural cast of the interior of the brachial valve. 

 The exterior of the pedicle-valve. 



A natural cast of a pedicle-valve ; showing the high cardinal area, the convex deltidium, the fill- 

 ing of the rostral cavity and the vascular sinuses in the pallial region. 

 Potsdam sandstone. Lake Pepin, Wisconsin. 



