PLATE XIc. 



(FiKures 1-3, 5-9, 13, U, 17, 18, 20-32 by K. P. WhitI'IELD; 4, 10-12, 15, 16, 10, 25-28 by E. Emmons; Zi, 24 by C. E. Beecheh; 



29-39 copied.) 



Legend. F. Foramen, il. Dental lamellae. 



ps. Deltidium. a. Anterior adductoi-s. 



c. Crura. a'. Posteiior adductors, 

 j. Cardinal process. r. Diductors. 



Genus TRIPLECIA, Hall. 



Pase 269. 



Tkiplecia extans, Emmous. 



Fig. 1. The brachial valve of an individual of average dimensions. 

 Fig. 2. An anteiior view of the same. 



Fig. 8. A cardinal view of the same. The delthyrium, which is hei-e repi-esented as open, is obscured in 

 the specimen. 



Trenton limestone. Lomrille, N. Y. 

 Fig. 4. The cai'dinal area of the pedicle-valve ; showing the apical foramen and the convex deltidial 

 cove)'ing. 



Ti-enton limestone. Carlton Ishnid, N. Y. 



Fig. 5. A cardinal view of a bi-achial valve ; showing the bifurcated cardinal process extending into 



the matrix. 

 Figs. K, 7. Anterior and posterior views of a normal individual, the latter showing the impressions of the 



denial plates of the pedicle-valve. X 2. 



Trenton limestone. MiddlevUle, N. Y. 



Triplegia nucleus, Hull. 



Figs. 8, 9. Cardinal and profile views of a normal in<lividual, the former showing the foi'amen and <leltid- 

 ium of the pedicle-valve. X 2. 



Trenton limestone. MiddlevUle, iV. Y. 



Tkiplecia spirifekoides, McCoy. 



Fig. 10. An intei'nal cast of the l)rachial valve. 



Fig. 11. A cai-dinal view of the same specimen ; showing the impressions of the ci-ui-a (c) and of the bifur- 

 cated cardinal process. 



Caradoc sandstone. Niyrth Wales. 



Triplegia Ortoni, Meek. 



Fig. 12. The interior of the pedicle-valve ; showing the narrow area and much thickened teeth. 



Fig. 13. The exterior of a brachial valve. 



Fig. 14. Cardinal view of a specimen having the valves in conjunction ; showing the cardinal area, fora- 

 men and deltidium. 



Fig. 1.^. Intei'ior of the cardinal I'egion of conjoined valves ; showing their mode of articulation. 



Fig. 16. Pi'otile of the apical portion of the brachial valve ; showing the curvature of the cardinal process. 



Fig. 17. The central cardinal portion of an old and thickened bi-achial valve. The tips of the cardinal 

 process and of one of the crura have been broken. 



Fig. 18. The external cai-dinal area of conjoined valves. X 3. 



Fig. 19. Posterior view of the cardinal process ; showing the grooves on the outer face of its branches. 



Fig. 20. Inner view of the same feature in a youngei' shell. 

 Clinton group. Dayton, Ohio. 

 For other illustrations, see Palteontology of Ohio, Volume I, plate xv, tigs. 1 a-k. 



Triplegia insularis, Eichwald. 



Fig. 21. Posterior view of an intei-nal cast of the conjoined valves; showing, in the brachial valve, the im- 

 pressions of the anterior and postei-ior adductoi's, the crura and cai-dinal process, and, in the 

 pedicle-valve, the extent of the dental lamellas. 



Caradoc sandstone. Ty-Isaf, Wales. 



