PLATE LXVII. 



(Kiguies 1, 2, U-IH by E. EMMONS ; 3-10, 20 liy G. I!. SIMPSON.) 



Genus CONCHIDIUM, Linne. 



Page 231. 

 CONCHIDIUM (?) OCCIDENTALIS, Hull. 



Figs. 1, 2. Ventral iiml pruKlc views of a specimen retaining- a iiortion of the .«liell in a somewhat mace- 

 rated condition ; showing the form of the species and faint traitea of plications over the 

 anterior siii-face. 



Fig. 3. A portion of the extei-ior surface enlarged ; sho%ving 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 impre.ssions of 

 the septal plates in the brachial valve. 



Guelph dolomites. Gait, Ontario. 



CONCHIDIUM SCOPAKIUM, SD. IIOV. 



Figs. 6, 7. Dorsal and venti'al \ lews of a specimen retaining much of the shell; showing the outline of 

 the species and preserving a very distinct and rather fine radial plication. 

 Guelph dolomites. Dwrham, Ontario. 



CONCHIDIUM OBSOLETUM, Sp. IIOV. 

 Figs. 8, 9. Venti'al and dorsal views of an internal east of a species pos.sessing a few low and broad plica- 

 tions. The figures show the length of the median septum in the pedicte-valve, and the position 

 of the septal plates of the brachial valve, and also the adductor muscular scai-s of the latter, 

 a feature which is rarely retained with distinctness in this genus. 

 Niagara dolomites. Getwa, Ottawa county, Ohio. 



Genus PENTAMERUS, Sowerby. 



Page 236. 



Pentamerus PERGIBBOSUS, Hall and 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, greater width than the supporting septum. 

 Niagara dolomites. Near Chicago, Illinois. 

 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 ^ew 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. IVwcoimn. 

 Fig. 17. Profile of a small and gibbous internal cast, having somewhat the form of the P. obloiigu.'i, var. 



Maquoketa (see tigs. 11-13), but less regularly convex. 

 Figs. IS, 19. Cardinal views of internal casts ; showing the variation in the convexity of the valves and 

 the position of the internal apophy.ses 



Niagara dolomites. Near Milwaukee, Wisconsin. 



