PLATE LXXXIII. 



(Figures 1-8, 12, 13, 26-41 by G. B. Simpson ; 9 by C. K. Bkecher ; In, n by It. 1'. Wimtfikld ; ll-23by K Khmuk« ( 



Genus EICHWALDIA, Billings. 



Piise 307. 

 ElCIIW.\LI)I.\ SCHIKIGONALI.-^, Billill';-.--. 



Fig. 1. Doi'.sal view (if conjoineil valves, till' l)nicliiiil valve being so broken jis to expose the median 

 septum. 



Figs. 2-4. Doi-sal, cardinal and front views ; showing the .smooth surface, and the " bare spot," or ped- 

 icle aperture. These figures are from the oHginal specimens of the species. 

 Black River limestone. Pauijuette's Rapids, Canada. 



ElCHW.VLDI.V CO.NCMXNA, Hall. 



Fig. 5. Dorsal view of tin- original specimen. 



Niagara gi-oup. Perry county, Teime-ssee. 



ElCHWALDIA GIBBOSA, Hall. 



Fig. (5. Dorsal view of the original specimen. 



Fig. 7. An enlargement of the external surface, showing the pimctic. X S. 

 Niagara group. Perry county, Teimessee. 



ElCHWALDIA RETICULATA, Hall. 



Fig. 8. The interior of the umbonal portion of the pedicle-valve ; showing the ti-iangular intei-nal apical 

 plate. X 2. 



Fig. 9. Dor.sal view of the youngest specimen oliserve J. X 10. (After Beechek and C'i.akkk, Memoira 

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



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

 chai'acter of the external surface. X 2. 



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

 eral margins. X 2. 



Fig. 13. The interior of a bi'achial valve ; .showing the cardinal j^rocess and the marginal gi'ooves for the 

 reception of the ridges on the opposite valve. X 2. 

 Niagara gi-oup. Waldron, Indiana. 



Genus AULACORHYNCHUS, Dittmak. 



Page 311. 



AuLACORHYNCHUS MILLEPUNCTATUS, Meek ami Wortlien. 



Fig. 14. The exteidoi' of a pedicle-valve, from which a portion of the shell has been exfoliated, showngthe 



inner sui-face of the triangular muscular platform. 

 Fig. 15. A very large brachial valve; showing tlje outline and sui-face characters. 

 Coal Measures. Croo/ced Creek, lllhwis. 



Genus TRIPLEGIA, Hall. 



Part 1, page 269. 



Triplegia Niagarensis, .>]). nov. 



Figs. 16-19. Cardinal, profile, obliiiue cardinal and front views of an internal 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 cai-dinal prt cess. 



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

 showing the bifurcated cardinal process and the teeth. X ^■ 

 Niagara dolomites. Near Milwaukee, Wisconsin. 



