PLATE L. 
(Figures 1-5 copies; 6, 8, 12-14, 26-31, 41-18, 51, 52 by E. Emmons; 7, 9-11, 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, 50 by R. P. Wiiiteield ) 
Legend: t. Teeth. b. Dental sockets. s Median septum (jiedicle-valve). 
d. Dental plates. c. Crura. s'. Median septum (brachial valve), 
hp. Hinge-plate. 
Genus EETZIA, King. 
Page 103. 
Eexzia Adrieni, de Verneuil. 
Figs. 1, 2. Dorsal and ventral views of a typical sjiecimen ; showing the characters of the exterior. 
Fig. 3. A doi'sal view of a smaller example, fi’om which a portion of the brachial valve has been removed, 
exposing the median septum and a portion of one of the sjiiral cones. 
Fig. 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 septum. 
Fig. 5. The interior of a xiortion of the brachial valve ; showing the hinge-plate and median septum. 
The above figui’es are copied from QUhlert, Annales Sci. Geol., t. xix. No. 1. 1886. 
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. Departement de la Sarthe, France. 
Genus PTYCHOSPIEA, gen. nov. 
Page 112. 
Ptychospira eerita, you Buch, 
Fig. 10. A profile view of an average individual; showing the coarse plication, and the extension of the 
anterior margin. X 2. 
Fig. 11. A dorsal view of the same specimen ; showing the coalesced deltidial plates. X 2. 
Middle Devonian. Eifel, Germany. 
Ptychospira longirostris, Kayser. 
Fig. 12. A dorsal view of a specimen ; showing the narrow and elevated beak of the pedicle-valve. 
Middle Devonian. Eifel, Germany. 
Ptychospira (cf.) sexplicata, White and Whitfield. 
Figs. 13, 14. Dorsal and venti al views of a specimen, probably I'eferable to this species. 
Bui-lington limestone. Burlington, Iowa. 
Subgenus HOMCEOSPIEA, s.-gen. nov. 
Page 112. 
Homosospira evax, Hall. 
Fig. 15. A doj-sal view of the youngest shell observed. In this stage of giowfh the beak of the pedicle- 
valve is erect and the deltidial plates net developed ; the sui'lace of the valves is smooth and 
evidence of plications is visible only outside of the second concentric gi-owth-line X 25. 
Figs. 16, 17. Prohle and doi-sal views of a full-grown specimen ; showing the adult charactei-s of the extei'ior. 
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. 
Fig. 19. A similar view of a more 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 EHYNCHOSPIEA, Hall. 
Page 108. 
EhYNCHOSPIRA FORMOSA, Htlll. 
Fig. 21. A dorsal view of a typical specimen ; showing the chai'acter of the exterior. 
Fig. 22. The interior of the cardinal portion of the pedicle-valve of a noi-mal adult; showing the circular 
foramen, the completely coalesced deltidial plates, and the teeth. X 2. 
Fig. 23. The interioi- of a pedicle-valve ; showing similar characters with less detail. 
Fig. 24. The interior of a brachial valve ; showing the form of the hinge-plate, the dental sockets and the 
median septum. 
Fig. 25. An interior view of the cardinal portion of ai'ticulated 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 Helderhergs, N. Y. 
