PLATE LXVI. 
(Figures 1-5, 11,13, 14, 16-19, 23-25 by E. Emmons ; 6, 8, 10 by R. P. Wiiitfielu ; 7, 9 by P. S. Swinton ; 12, 20-22 
by u. B. Simpson.) 
Genus CONCHIDIUM, Linne. 
Page 231. 
CONCHIDIUM UNGUIFORMIS, Ulricll. 
Figs. 1-3. Dorsal, cardinal and ventral views of the original specimen ; showing the form of the shell, the 
character of its [plication, its concentric varices and line growth-lines. The drawings ai'e 
slightly restored in the umbonal region of the pedicle-valve. 
Fig. 4. A lateral view of the same specimen, in which the median septum and spondylium of the pedicle- 
valve are exposed. 
Niagara group. Newr Louisville, Kentucky. , 
CONCHIDIUM, sp. indet. 
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 Mihcaukee, Wisconsin. 
CONCHIDIUM EXPONENS, Sp. IIOV. 
Figs. 6-9. Intei-iors of pedicle (tig-s, 6, 7) and brachial (tigs. 8, 9) valves of a strongly costate shell; showing 
the structure of the interior. 
Niagara group (Halysites bed). Louwville, Kentucky. 
CONCHIDIUM MULTICOSTATUM, Hull. 
See Plate 64. 
Fig. 10. A profile of the original specimen, an internal cast. 
Niagara dolomites. Wammufosa, Wisconsin. 
CoNCHiDiuM bilocul^Re, Liuiie. 
Fig. 11. Dors(il view of an average example ; showing- the form of the shell, character of the surface, and 
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 Gotland. 
CoNCHiDiuM DECUSSATUM, Wliiteavcs. 
See Plate 65, figs. 1.2. 
Fig 15. Doi-sal view of a small example ; showing the form and exterior characters of the species. 
Niagara dolomites. Rapids of the Gaskatcliewan River, British Avierica. 
CONCHIDIUM CoDLETTi, Miller. 
Figs 16, 17. Ventral and profile views of a pedicle-valve; showing the fine plication, frequent imbricating 
growth-varices, and the expanded anterior margin. 
Niagara limestone. Indiana. 
CONCHIDIUM Georgia!:, s[). uov. 
Figs. 18, 19. Dorsal and cai-dinal views of the brachial valve ; showing the consjiicuous median fold and 
the plication of the surface. 
Clinton group. Ti'cnton, Geos-gia. 
