PLATE XIc. 



KFiirurcs 1-3, 5-9, 13, 14, 17, 18, iO-iilljv K. 1'. WhitfiBLI); 4, 10-12, 15, 16, 1!), 2S-28 by E. Kmmo.ns; i), 24 by (J. E Beecher; 



2a-39 copies.) 



Legend. F. Foramen, <i. Dental lamella;. 



ps. Deltidiiim.  a. Anterior a(l(lu<'.tni-s. 



c. Ciura. a'- PiLsteiior aiiductoi-s. 



j. Cardinal process. r. Diductors. 



/   • 



Genus TRIPLEGIA, Hall. 



Pase 2()9. 



Tkiflecia extans, Emnious. 



Fig. 1. The brachial valve of an individual of average dimen.sions. 

 Fig. 2. An anterior view of the same. 



Fig. '^. A cardinal view of the same. The delthyrinni, whirh is here repi-esented as open, is oKsciired in 

 the specimen. 



Trenton limestone. Onoville, N. Y. 

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

 coveiing. 



Trenton limestone. Carlton Ishnid. N. T. 

 Fig. 5. A cai-dinal view of a brachial valve ; showing the bifnrcated cardinal process extending into 



the matrix. 

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

 dental plates of the pedicle-valve. X 2. 



Ti-entoii limestone. Middlevllle, N. Y. 



TlilI'Lf:ClA NUCLEUS, Hill I. 



Figs. 8, 9. Carilioid and jirotile views of a normal individnal, the former showing the foramen and deltid- 

 ium of the peilicle-valve. X 2. 



Trenton limestone. Middleville, N. ¥. 



Triplegia si'irifekoides, McCoy. 



Fig. 10. An internal cast of the lii'achial valve. 



Fig. 11. A cai'diiial view of the same specimen ; showing the impressions of the crura (c) and of the bifur- 

 cated cardinal process. 



Caradoc sandstone. Nirrth Wales. 



TKiPLEfUA Ortoni, Meek. 



Fig. 12. Tlie interior of the peilicle-valve ; showing the narrow area and much thicliened teeth. 



Fig. 13. The exterior of a brachial valve. 



Fig. 14. Cardinal view of a specimen having the valves in (MnjiUKttion ; showing the cardinal aiea, fora- 

 men and deltidium. 



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



Fig. 11). Protile of the apical i)Oition of the brachial valve ; showing the cni-vatnre of the caniinal process. 



Fig. 17. The central cardnial portion of an old and thickened brachial valve. The tips of the cardinal 

 lirocess and of one of the crura have been broken. 



Fig. IS. The external cardinal area of conjoined valves. X 3. 



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



Fig. 20. Inner vievv of the same feature in a younger shell. 

 Clinton group. Dayton, Ohio. 

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



Triplegia insularis, Eic-hwald. 



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

 jiressions of the anterior and posterioi' adductors, the crura and cardinal process, and, in the 

 pedii^le-valve, the extent of the dental lamella;. 

 Carailoc sandstone. Ty-Isaf, Wales. 



