PUA^TE XLVI— CohUnaod. 

 Fly. 18. The exterior of a jkhUcIc- valve ; showing the normal marginal outline of the species. 

 Fig. 18. The exterior of a large l)iiichiAl valve with few and ilistaut lamella; and unusually extended 

 hinge-line. The firet of these lamella; bears a serrated margin, while the rest are regular. 

 The anterior and lateral margins of the valve are concealed by the great expansion of the 

 submarginal lamella. 



Keokuk group. CrawfordsvUU, Indiatia. 

 Fif. 90. The central cardinal |>ortion of an internal cast of conjoined valves, enlarged ; showing the posi- 

 tion of the teelh, dental plates and hinge-plate, the filling of the pedicle- cavity and visceral 

 foramen, the latter being traversed for its entire length by a median groove, representing a 

 faint median ridge ujwn the brachial valve, extending fi-om the ajiex across the muscular 

 area. X 3. 



Waverly group. SciotovUh, Ohio. 



Athvris INCRASSATA, Hilll. 



Fig. 21. The exterior of a somewhat weathered pedicle-valve. 

 Burlington limestone. Burlingtmi, Iowa. 



Genus SPIRIFER, Sowerby. 



Page 1. 

 Fig. 22. This figure is an enlarged repre8enta.tion of an internal cast of a small pedicle-valve belonging to 

 a species of Spirifbr similar to S. psmidolineatus. Hall. This fossil occurs in the soft shales of 

 the Waverly group, and its generic charactera are usually obscured. Its relation to Spiriper 

 is indicated by the long, thin denial lamellse, low median septum, and fine surface spines which 

 are ]>lainly double-bari-elled at the base. Additional specimens obtained since this plate was 

 engraved show that these spines bear series of short lateral branches. 

 Waverly grroup. Richfield, Ohio. 



Genus ATHYRIS, McCor. 



Pago 83. 



Subgenus CLIOTHYRIS, King. 

 Cliothyris Rotsii, Levcille. 



Fig. 28. Dorsal view of conjoined valves ; showing the concentric rows of flat spines. X 2. 



Keokuk group. Keokuk, lovoa. 

 Fig. 24. An enlargement of a portion of the surface. 



Chester limestone. Jackson arunty, Kentucky. 



Cliothyris hirsuta, Hall. 



Fig. 25. Dorsal view of an average specimen denuded of its spines. X 2. 



Fig. 26. A larger specimen with portions of the rows of flat spines adhering. X 2. 



Fig. 27. View of the hinge-plate ; showing the crescentiforra wall made by the crural lobes, and the thick 



central lobe of the plate. X B. 

 Fig. 2S, The same B|>ecimen viewed from in fi-ont ; showing the elevation of the hinge-plate, the ci-ural 



baaes and the minute visceral foi-amen which is usually closed in its upward extension. X 5. 

 St. Louis limestone. BUxnnington, Indiana. 



