PLATE LIII. 



(Figures 1-3, 5-7, 11-13, 17-23, 29,30, 36-38, 46, 48, 84, 65 by (i. B. Simpson; 4 by J. M. Clakkk; 8, 9, 14, 18, 31, 40-4-2, 45, 

 47, 49, 51, 53 by E. Emmons; 10, 16, 24-28, 32-34, 39 by R. P. Whitfield; 43, 44, 50, 62 by F. B. Meek ) 



Genus ATRYPINA, gen. nov. 



Page 161. 



Atrypina disparilis, Hall. 



Figs. 1-3. Ventral, profile and dorsal views of an average nialuie example; showing- the plano-convex 



contour, spai-se plication and concentric sui-face markings. X 2. 

 Fig. 4. A doi-sal 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 imbrtcata, Hall, 



Fig. i). The interior of a pedicle-valve ; showing the concave deltidial plates and the 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 bi-achial valve ; showing the bilobed cardinal process and a poi-tion of one of the 



spirals. X 2. 

 Fig. 9. A cardinal view of the same specimen ; showing a nai-row area and the size of the cardinal 



process. X 2^. 

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



nearly enclosed by the substance of the valve, and the lamella of the surface. X S. 

 Lowei- Helderberg group. Near Clarksmlle, N. Y. 



Genus CCELOSPHIA, Haix. 



I'aKe l;!4. 

 CtELOSPIRA PLANOCONVEXA, Hull. 



See Plate 52. 



Figs. 11-13. Ventral, doi-aal ami ))rofiIe views of a specimen, natural size ; showing the contour and surface 

 characters of the shell. 



Fig. 14. The intenor of a bi-acliial valve ; showing the form of the cardinal process and the thickened 

 median ridge. X 2. 



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

 inal process. X 5. 



Fig. 16. The interior of an incomplt-te brachial valve; showing cardinal process, dental sockets, and the 

 muscular depressions on either side of the thickened median ridge; enlarged. 

 Clinton grouji. HamilUm, Ontario. 



Genus ATRYPINA, gen. nov. 



Page 161. 



Atrypina Clintoni, sp. iiov. 



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



muscular i-idge. X 3. 

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



rostral cavity of the i)edicle-valve. X 2. 

 Fig. 18. An internal cast of the pedicle-valve ; showing the adductor and diductor muscular scai-s. X 2. 

 Fig. 19. The exteiior of a pedicle-valve. X ii. 



Clinton group. Drift of western Neio York. 



Genus CGELOSPIRA, Hall. 



Page 134 

 CfELOSPIRA CONCAVA, HilU. 

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

 Fig. 21. The exterior of a bi-achial valve ; showing its concavity and the posterior portion of the carilinal 



process. X 2. 

 Pig. 22. The interior of the bra -hial valve ; showing the character of the cardinal process and socket-walls, 



and the median thickening between the musculai- impressions. X 3. 

 Fig. .23. The intenor of an incomplete pedicle-valve ; showing the open delthyrium, the teeth and muscu- 

 lar impressions. X 3. 



Lower Holdei-berg group (Shaly limestone). Near Clarksville, N. Y. 



