PLATE XIc. 



|(KiK«rcs 1-3, 5-fl, 13, 14, 17, iS, iO-iMlby K. I". WnnriEl.1); i. 10-12, 15, Ifi, l:i, 25->8 by E. Emmons; 'iS, 24 by C. E. Beecher; 



2U-39 copies.) 



Legend. F. Foniiueii, il. Dental lanielliE. 



ps. Delticiiiini. a. Anterioi- adducUn-.s. 



c. Crura. a'. Posterior adductors, 



j. Cariliual [irocess. r. Diductors. 



Genus TKIPLECIA, Hall. 



Page 2fi9. 



Tkiplecia extans, Emmons. 

 Fig. 1. The bia<rhial valve of an individual of average dimensions. 

 Fig. 2. An anterior view of the same. 



Fig. 3. A cardinal view of the same. The delthyriuni, whiuh is here represented as open, is obscured in 

 the specimen. 



Trenton limestone. Lowville, N. ¥. 

 Kig. 4. The cardinal area of flie pedicle-valve ; showing the apical foramen and the convex deltidial 

 covering. 



Ti-enton limestone. Carlton Islrni.d, N. Y. 



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



the matrix. 

 Figs, t), 7. Anterior and posterior views of a normal imlividual. the latter showing the impressions of the 



dental plates (if the pedicle-valve. X 2. 



'I'renton limestone. MiddleinUe, N. Y. 



Tkiplecia nucleus, H:ill. 



Figs. 8, n. Cardinal and profile views of a normal individual, the former showing the foramen and deltid- 

 ium of the pedicle-valve. X 2. 



Trenton limestone. Middleville, N. Y. 



Triplegia spikikekoides, McCoy. 



Fig. 10. An intei'nal (^ast of the brachial valve. 



Fig. U. A cardinal view of the same specimen ; showing the impi-essions of the crui'a (c) and of the bifur- 

 cateil cardinal process. 



C'ai'adoc sandstone. North Wales. 



Tkiplecia Outoni, Meek. 



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

 Fig. 18. The extei-ior of a brachial valve. 



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

 men and deltidium. 

 Fig. 1."). Interior of the cardinal region of conjoined valves ; showing their mode (jf articulation. 

 Fig. 11). Pi-otile of the apical portion of the brachial valve ; showing the curvature of the cardinal process. 

 Fig. 17. The (-enti-al i-ai-dmal jiorlion of an old and thickened brachial valve. The tips of the cardinal 



process and of one of the ci-ui-a have been bi-oken. 

 Fig. 18. The external cardinal area of conjoined valves. X 'A- 



Fig. 19. Posterior view of the cardinal proces.s ; showing the grooves on the outei- face nf its branches. 

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

 Clinton group. Dayton. Ohio. 

 For othei- illustrations, .see Palasontology of Ohio, Volume I, jilate xv, tigs. 1 a-k. 



Tkiplecia insulakis, Eicliwuld. 



Pig. 21. Posterior view()f an internal cast of the conjoined valves; showing, in the brachial valve, the im- 

 pressions of the antertor and postei-ior adductor.^, the crura and cardinal proce.ss, and, in the 

 pedicle-valve, the extent of the dental lamelUe. 

 (-'aradoc .sandstone. Ty-lsaf, Wales. 



