28 



SMITHSONIAN INSTITUTION 



2. S. spinifer n. sp. 



3. 5". mutabilis n. sp. 



4. 5". stellatus (Hall). 



Calyx rather narrowly elongate. 



Plates deeply sculptured ; with sharp continuous 

 costae from base up, surmounted with slender 

 spines. 



IIBr about 12; median ridge narrow. 



Linden formation, Tennessee. 

 Calyx variable, usually shorter than wide. 



Lower part of cup turbinate, with sides usually some- 

 what convex. 

 Plates low-convex, usually without strong stellate 

 sculpture, but with crenulate margins and pits 

 at corners ; rarely spiniferous. 



IIBr about 12 to 15; median ridge broad. 

 Decatur and Linden formations, Tennessee. 

 Calyx rather short, height to width about equal. 



Plates low, more or less rugose, with prominent 

 connecting ridges alternating with deep pits 

 above, producing strongly stellate sculpture. 

 IIBr about 10; median ridge narrow. 



Keyser limestone, West Virginia. 

 B. Calyx widest below IIBr, contracting and cylindrical toward 

 arm-bases. 



iBr areas protuberant. 



Calyx broad, robust, extremely large, about as wide as 

 high. 



Plates smooth, broadly convex, often obtusely pus- 

 tulose. iBr areas sharply protuberant and IBr 

 deeply depressed between them. 



IIBr about 12; median ridge broad. 5. 5". pratteni (McCh.). 



Linden formation, Tennessee. 

 Calyx elongate, large. 



Plates strongly convex, with obtuse stellate sculp- 

 turing, not pustulose. iBr areas obtusely pro- 

 tuberant. 



IIBr 13 to 15 ; median ridge rather narrow. 



6. .9. pyburnensis n. sp. 

 Linden formation, Tennessee. 

 Plates smooth and flat, some with pustulose center. 

 Lower part of calyx broadly curving at wide 



angle from base. 



IIBr about 11; median ridge narrow. 



Haragan limestone, Oklahoma. 

 Calyx small, spheroidal below IIBr. iBr areas not 

 protuberant. 



Plates gibbous, thick, smooth to obtusely stellate. 

 IIBr about 11 ; median ridge narrow. 



Haragan limestone, Oklahoma. 



7. S. ulrichi (Sch.). 



8. 5". gibbosus n. sp. 



The species of group A are directly comparable with the Bohemian forms 

 of that type; while those of group B are of a facies totally different from any 



