8 ANNALS NEW YORK ACADEMY OF SCIENCES 



to conceive how such a configuration as that of M. buttersi might be 

 evolved from that of Worthenia tabulata. The sculpture also appears to 

 be of the same general character, the most essential difference being the 

 development of transverse costse and of revolving lirse more prominent 

 than the rest on the lower half of the inferior zone. Some important 

 characters of M . buttersi are still unknown, but if these show no addi- 

 tional differences, it may prove to be a rather extreme form of Worthenia. 

 Hoeizon and locality: Lykins formation; Heygood Canyon, Colo- 

 rado (lots 3264 and 3266). 



