ABSTRACTS OF PAPERS 135 



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The following species evolved : S. callaicayensis Swallow : Shell thick, 

 coarsely plicate, hinge longer than greatest width of shell. ^. hoonensis Swal- 

 low : Shell thick, coarsely plicate, strongly convex. S. equicostata Swallow : 

 Shell thin, hinge shorter than greatest width of shell, finely plicate. S. cym- 

 hiformis Swallow : Shell thin, hingeline very short, finely plicate, iinibo pro- 

 jecting prominently behind hingeline. S. inffexa Swallow : Shell thick, hinge- 

 line shorter than greatest width of shell, umbo projecting prominently behind 

 hingeline. >§. navalis Swallow : Shell thick, coarsely plicate, very convex, im- 

 perfectlj^ developed carinate fold. 



The University of Missouri has more than 2,000 specimens of Snyder Creek 

 stropheodonts and series have been arranged showing minute variations from 

 S. demissa (Conrad) to each of the species listed above. The intermediate 

 grades are rare, while there are large numbers of the typical forms. 



All of the new species disappeared before 50 feet of Snyder Creek shales 

 had been deposited. 



The Societ}' then adjourned. 



