PLATE LXVI. 



(Figures 1-5, 11, 13, 14, 1«-1H, -ii-irt by E. Emmons ; H, s, 10 by K. P. Whitkield ; 7, '.t by F. S. Swinton ; 12, 20-22 



by U. B. Simpson.) 



Genus CONCHIDIUM, Linne. 



Page 231. 

 CONCHIDIUM UNGUIFORMIS, Ulricll. 

 Figs. 1-3. Doi'sal, cardinal and ventral views of the original specimen ; showing the form of the shell, the 

 character of its [plication, its concentric varices and tine growth-lines. The drawings ai-e 

 slightly restored in the umbonal region of the pedicle-valve. 

 Pig. 4. A lateral view of the same specimen, in which the median septum and spondylium of the pedicle- 

 valve are exposed. 



Niagara group. Near Loui.iville, Kentucky. 



CONCHIDIUM, sp. iiidet. 



Fig. 5. An internal cast of a small pedicle-valve, with a coarsely plicated surface ; showing the apical 

 portion of the tilling of the spondylium and a somewhat distorted median septum. 

 Niagara dolomites. Near MiliDaukee, Wisconsin. 



CONCHIDIUM EXPONENS, Sp. IIOV. 



Figs. 6-9. Interioi-s of i>edicle (figs, 6, 7) and brachial (tigs. 8, 9) valves of a strongly costate shell ; showing 

 the structure of the interior. 



Niagara group (Halysites bed). LouistiUe, Kentucky. 



CONCHIDIUM MULTICOSTATUM, Hall. 

 See Plate 64. 

 Fig. 10. A profile of the original specimen, an internal cast. 



Niagara dolomites. Wamcaiitosa, Wisconsin. 



CONCHIDIUM BILOCULARE, LilUlC. 



Fig. 1 1 . Dorsal view of an average example ; showing the form of the shell, character of the surface, afld 



retaining a portion of the deltidium. 

 Fig. 12. A profile of the same specimen ; showing the long, concave and smooth cardinal slopes. 

 Fig. 13. A natural longitudinal section of conjoined valves; showing the relation of the spondylium and 



septal plates. 

 Fig. 14. Ventral view of the same individual ; showing the length of the median septum. 

 Upper Silurian limestone. Island of ffotland. 



CONCHIDIUM DECUSSATUM, WhitcaVCS. 

 See Plate 65, tigs. 1. 2. 

 Fig 15. Dorsal view of a small example ; showing the form and exterior characters of the species. 

 Niagara dolomites. Rapids of the t^a^katchewan River, British Ainerica. 



CONCHIDIUM CoLLETTi, Miller. 



Figs 16, 17. Ventral and profile views of a pedicle-valve ; showing the tine plication, frequent imbricating 

 growth-varices, and the expanded anterior margin. 

 Niagara limestone. Indiana. 



CONCHIDIUM GEORGIJi, sp. llOV. 

 Figs. 18, 19. Dorsal and cardinal views of the brachial valve ; showing the conspicuous median fold and 

 the plication of the surface. 



Clinton group. Trenton, Georgia. 



