XXVIl] PTILOZAMITES 547 



rib, while a median vein frequently occurs in those of Thinn- 

 feldia. There can be little doubt as to the very close alliance 

 between the Rhaetic species referred to these two genera. The 



Fig. 361. Ptilozamites Heeri, Nath. (^ nat. size. After Nathorst.) 



