PLATE LXXXIII. 



(Figures 1-8, 12, 13, 26-41 by G. B. SIMPSON ; 9 by C. E. Beecher ; 10, 11 by K. P. Whitfield ; U-23by E Ehmuns ) 



Genus EICHWALDIA, Billings. 



Page 307. 

 ElCHWALDIA SUBTKIGONALIS, BillillgS. 



Fig. 1. Dorsal view of conjoined Talves, the brachial valve being' so broken aa to expose the median 

 septum. 



Pigs. 2-4. Dorsal, c-ardinal and front views; showing the smooth surface, and the "bare spot," or ped- 

 icle aperture. These tij^ures are from the original specimens of the species. 

 Black River limestone. Pauqiuite's Rapids, Canada. 



ElCHWALDIA GONCINNA, Hilll. 



¥ig. 5. Dorsal view of the original specimen. 



Niagara group. Perry cotiniiy, Tennessee. 



ElCHWALDIA GIBBOSA, Hall. 



Rgf. 6. Dorsal view of the original specimen. 



Fig. 7. An enlargement of the external surface, showing the punctse. X 5. 

 Niagara group. Perry county, Tennessee. 



ElCHWALDIA KETICHLATA, Hilll. 



Pig. 8. The interior of the umbonal portion of the pedicle-valve ; showing the triangular internal apical 

 plate. X 2. 



Pig. 9. Dorsal view of the youngest specimen observed. X 10. (After Bbechbr and Clarke, Memoirs 

 N. Y. State Museum, Vol. 1, No. 1.) 



Figs. 10, 11. Cardinal ami ilorsal views of an average specimen; showing the pedicle-aperture and the 

 character of the external surface. X 2. 



Fig. 12. The interior of the pedicle-valve ; showing the open delthyrium and the linear ridges on the lat- 

 eral margins. X 2. 



Fig. 13. The interior of a bra<-hial valve ; showing the cardinal process and the marginal grooves for the 

 reception of the ridgi's on the opposite valve. X 2. 

 Niagara gi-oup. fValdrun, Indiana. 



Genus AULACORHYNCHUS, Dittmak. 



Page :ill. 



AuLACORHYNCHUs MiLLEPUNCTATUS, Meek aiicl Woitheii. 



Fig. 14. The exterior of a pedicle-valve, from which a jiortion of the shell has been exfoliated, showing the 



inner surface of the triangular muscular platform. 

 Fig. 15. A very large brachial valve ; showing the outline and surface charactei-s. 

 Coal Measures. Crooked Creek, Illinois. 



Genus TKIPLECIA, Hall. 



Part 1, page 269. 



Triplkcia Niaoarensis, Sp. IIOV. 



Figs. 16-19. Cardinal, profile, obli<iue cardinal and front views of an intenial cast; showing the sharply 

 defined median fold and sinus on brachial and pedicle-valves respectively, the marginal plica- 

 tion, and the cavity left by the cardinal pricess. 



Fig. 20. View of the articulating processe.*, taken from a gutta-percha impression of the same specimen ; 

 showing the bifui-cated cardinal proces.'i and the teeth. X 5. 

 Niagara <lolomites. Near Milwaukee, Wisc(yasin. 



