PLATE L. 



igures 1-5 copies; 6 8, li-U. 26-31, 4I-«8 51, 5-3 by E. Emmons; 7, S-11, 16, 17, 20. 22, 24, 32-35 by G B SIMPSON- 

 15, 18, 19 by J M. Clakke; 21 by F. B. Meek; 23, 25, 36-40, 49, 60 by R. P. Whitfield ) '""'^*<"'' 



Legend : t. Teeth. b. Dental sockets. s Median eeptum (nedicle-valve). 



h Hi" e lat ''■ ''^'"*' ^'' '^^'"'^" septum (brachial valve). 



Genus RETZIA, King. 



Page 103. 



Retzia Adrieni, de Verneuil. 



Figs. 1, 2. Doi-sal and ventral views of a typical sj.ecimen ; showing- I he charactere of the exterior 



Hg. 6. A dorsal view of a smaller example, from which a poi-tion uf the brachial valve has been removed 



exposing the median septum and a portion of ( ne of the spiral cones. ' 



*1g. 4. An enlarged view of a shell which has been transversely sectioned just in front of the umbones- 



showing- the hinge-plate, dental sockets and median seiitum. ' 



Fig. 5. The interior of a portion of the brachial valve ; showing the hinge-plate and median septum. 

 TO o f°?*'"'^^°&"'«'«''''« ™I'ied from CEiiLERT, AnnalesSci. Geol., t. xix, No. 1. Iis86 



Fig. 6. A dorsal view of a somewhat flattened example. 

 Fig. 7. A more rotund individual, imperfect about the ante-lateral margin. 

 Fig. 8. A view of a similar specimen of larger size. 

 Fig. 9. A dorsal view of the umbonal region of conjoined valves; showing the excavate cardinal slopes 



of the pedicle-valve and the concave coalesced deltidial plates. X 2. 

 Lower Devonian. Departeinent de la Sarthe, France. 



Genus PTYCHOSPIRA, gen. nov. 



PiiRe 112. 



Pttchospika FERrrA, voii Buch. 

 Fig, 10. A profile view of an average individual ; showing the coai-se plication, and the extension of the 



anterior margin. X 2. 

 Fig. 11. A dorsal view of the same B|)ecimen ; showing the coalesced deltidial ]>lates. X 2. 

 Middle Devonian. Bifet, Oermany 



Pttchospika lonoirostris, Kayscr. 



Fig. 12. A dorsal view of a specimen ; showing the narrow and elevated beak of the pedicle-valve. 

 Middle Devonian. Bifel, Oermany. 



Ptychospira (cf.) SEXPLiCATA, Wliito iiiid Whitfield. 



Figs. 13, 14. Dorsal and ventral views of a specimen, probably referable to this species. 

 Burlington limestone. Burlington, Itrwa. 



Subgenus HOMCEOSPIKA, s.-gen. nov. 



V&t^e Hi. 

 HOMCEOSPIRA EVAX, Hall. 

 Fig. 15. A doi-sal view of the youngest shell observed. In this stage of growth the beak of the pedicle- 

 valve is erect and the deltidial plates not developed ; the surface of the valves is smooth and 

 evidence of plications is visible only outside of the second concentric growth-line. X 25. 

 Figs. 16, 17. Profile and dorsal views of a full-grown .specimen ; showing the adult characters of the exterior. 

 Fig. 18. The umbonal region of a young shell in which the deltidial plates have united at the base, enclos- 

 ing an oval foramen. X 7. 

 Rg. 19. A similar view of a moi-e fully grown individual with unusually erect beak and nearly ovate 



foramen. X 3. 

 Fig. 20. The interior umbonal portion of a fully-matured example ; showing the complete obsolescence of 

 the deltidial plates and the enclosure of the foramen by the substance of the valve ; also the 

 projecting, recurved teeth. X 2. 



Niagara group. Waldron, Indiana. 



Genus RHYNCHOSPIRA, Hall. 



Page 108. 

 RhYNCHOSPIRA FORMOSA, Hall. 

 Fig. 21. A dorsal view of a typical si)ecimen j showing the character of the exterior. 

 Fig. 22. The interior of the cardinal portion of the pedicle-valve of a normal adult; showing the circular 



foramen, the completely coalesced deltidial jilate-s, and the teeth. X 2. 

 Fig. 23. The interior of a pedicle-valve ; showing similar charactera with less detail. 

 Fig. 24. The interior of a brachial valve j showing the form of the hinge-plate, the dental sockets and the 



median sentum. 

 Fig. 25. An interior view of the cardinal portion of articulated valves ; showing the elevation of the hinge- 

 plate, and the median septum of the brachial valve, and the muscular depression of the 

 pedicle-valve. X 2. 



Lower Helderberg group (Shaly limestone). The Helderbergs, N. Y. 



