PLATE LXVII. 
(Figures 1, 2, 11-19 by E Emmons ; 3-10, 20 by G. B. SiMPSON.) 
Genus CONCHIDIUM, Linne. 
Page 231. 
CONCHIDIUM (?) OCCIDENTALIS, Hall. 
Figs. 1, 2. Ventral and profile views of a specimen retaining a portion of the shell in a somewhat mace¬ 
rated condition ; showing the form of the species and faint traces of plications over the 
anterior surface. 
Fig. 3. A portion of the exterior surface enlarged; showing the irregular lamellose concentric growth 
lines and the faint radial plications. X 2. 
Fig. 4. Profile of the umbonal portion of both valves, that of the pedicle-valve retaining its normal con¬ 
tour and showing its great elevation, conspicuous incurvature and uniform contour. 
Fig. 5. Dorsal view of an internal cast of a somewhat distorted example ; showing the impressions of 
the septal plates in the brachial valve. 
Guelph dolomites. Galt, Ontario. 
CONCHIDIUM SCOPARIUM, SD. IIOV. 
Figs. 6, 7. Dorsal and venti-al views of a specimen retaining much of the shell; showing the outline of 
the species and preserving a very distinct and I'ather fine radial plication. 
Guelph dolomites. Dwrtiam, Ontario. 
CONCHlDlUM OBSOLETUM, Sp. IIOV. 
Figs. 8, 9. Ventral and dorsal views of an internal cast of a species possessing a few low and broad plica¬ 
tions. The figures show the length of the median septum in the pedicle-valve, and the position 
of the septal plates of the brachial valve, and also the adductor muscular scars of the latter, 
a feature which is i-ai-ely retained with distinctness in this genus. 
Niagara dolomites. Genoa, Ottaim county, Ohio. 
Genus PENTAMERUS, Sowerby. 
Page 23fi. 
Pentamerus pergibbosus, Hull uiid Whitfield. 
Fig. 10. A view looking into the umbonal cavity of conjoined valves; showing the spondylium and its 
supporting septum below, and the crural processes of the brachial valve above. The spondy¬ 
lium is extremely narrow and deep, having scarcely, gi-eater width than the supporting septum. 
Niagara dolomites. Wear Chicago, IlliTwis. 
Fig. 14. Cardinal view of an internal cast of a large individual; showing the relative depth of the valves 
and the cavities left by the spondylium and septa. 
Fig. 15. Profile view of a similar internal cast; showing the normal contour of the species. 
Niagara dolomites. Near Milwaukee, Wisconsin. 
Fig. 16. Cardinal view of an internal cast of a small shell, which shows with much distinctness the posi¬ 
tion and form of the deltidium. 
Chert of the Niagara group. Wiscon,sin. 
Fig. 17. Profile of a small and gibbous internal cast, having somewhat the form of the P. ohlongus, var. 
Maquoketa (see figs. 11-13), but less regularly convex. 
Figs. 18, 19. Cardinal views of internal casts; showing the variation in the convexity of the valves and 
the position of the internal apophyses 
Niagara dolomites. Near Milwaukee, Wisconsin. 
