PLATE LIII. 



(Figures 1-3, S-7, 11-13, 17--i3, 29, 30, 3(5-38, 4li, 48, 64, 65 by G. B. .Simpson; 4 by J. U Clakki;; 8, 9, 14, 15, 31, 40-4J, 45, 

 47, 411, 51, 53 l)y K. Emmons; 10, 16, '>4-28, 32-35, 39 by li. P. Whitfield; 43, 44, 60, 62 by F. B. Meek 1 



Genus ATRYPINA, gen. no v. 



Page lai. 



Atrypina disparilis, HiiU. 



Figs. 1-3. Ventral, protile and dor.sal v'ibw.'* of an average inaluie exani|ple; showing the plano-convex 



contour, sjianse plication and concentric surface markings. X 2. 

 Fig. 4. A dorsal view of a very young individual; showing the deltidial plates beneath the erect beak, 



the deep median sinus of the brachial valve and its low plications. X 5. 

 Niagara' group. Waldron, Indiana. 



Atrypina imbricata, Hall, 



Fig. .n. The interior of a pedicle-valve ; showing the concave delti<lial plates and (he teeth. X 2. 



Fig. 6. The interior of an incomplete pedicle-valve; .showing the deep pedicle-cavity. X 2. 



Fig. 8. The interior of a brachial valve ; showing the bilobed cardinal process and a portion of one of the 



spirals. X 2. 

 Fig. 9. A cai'dinal view of the same specimen ; showing a narrow area and the size of the cardinal 



process. X 2i. 

 Fig 10. The cardin.al region enlarged ; showing the slightly concave deltidial plates, the circular foramen 



neai-ly enclosed by the substance of the valve, and the lamella; of the sui-face. X .">. 

 Lower Helderberg grcnip. Near darksville, N. Y. 



Genus CCELOSPIRA, Halt,. 



l>;ii,'e 134. 



CfELOSPIRA PLANOCONVEXA, H;ill. 



See Plato :>2. 



Figs. 11-13. Ventral, dorsal and protile views of a specimen, natural size ; showing the contour and surface 



characters of the shell. 

 Fig. 14. The iutei'ior of a brachial valve; showing the form of the cardinal process and the thickened 



median i-iiige. X 2. 

 Fig. 15. A still further enlargement of a poition of the same valve, to show Ihe grooved lobes of the canl- 



inal proce.=!s. X .^. 

 Fig. 16. The interior of an incompl.-'te brachial valve : i^howing cardinal process, dental sockets, and the 

 muscular depressions on either side of the thickened median I'idge ; etdai'ged. 

 Clinton groii]>. Hamilton, (hitario. 



Genus ATRYPINA, gen. nov. 



ViViK 101. 



Atrypina Clintoni, sp. nov. 



Fig. 7. The interior of an incomplete brailiial valve ; shciwing the bilobed hinge-plate and the median 



muscular i-idge. X t>- 

 Fig. 17. A dorsal view of a specimen ; showing the internal cast of the brachial valve and the teeth and 



rostral cavity of the jiedicle-valve. X 2. 

 Fig. 18. An internal cast of the pedicle-valve ; showing the ailductor and diductor muscular scars. X 2. 

 Fig. ]!). The exterior of a jteilicle- valve. X 2. 



Clinton group. Drift of loestera New York. 



Genus CCELOSPIRA, Hall. 



Page 134 

 C(ELOSpira concaa'a. Hall. 

 Fig. 20. The exterior of a pedicle-valve. X 2. 

 Fig. 21. The exterior of a brachial valve ; .showing its concavity and the posterioi- p(n-tion of the cardinal 



process. X 2. 

 Fig. 22. The interior of the brachial valve ; showing the character of the cardinal process and socket-walls, 



and the median thickening between the muscular impressions. X 3. 

 Fig. .23. The interior of an incomplete pedicle-valve ; .showing the open delthyrinm, tlie teeth and muscu- 

 l.ar ini|n'essions. X 3. 



Lower Helderbei-g gronji (Shaly limestone). Near ClarkxmUe, N. T. 



