NO. 24 PTARMIGANIA STRATA RESSER 19 



of whatever kind than the same forms from adjacent areas. For 

 instance, the only granulose Kootenia species known — and several 

 hundred new species have been studied and described in manuscript — ■ 

 come from this area. Other trilobites behave in the same fashion. 

 Even the smooth forms such as Prosacanthoides develop strong 

 anastomosing lines on the elevated portions of the test. 



Species from other localities have been described. Some are 

 definitely from the Brigham and Langston formations. Others pre- 

 sumably represent the Ptarmigania fauna. Each will be readily 

 determinable if localities are noted. 



AGE OF THE PTARMIGANIA FAUNA 



The Ptarmigania fauna is evidently of early Middle Cambrian age. 

 Strong Lower Cambrian elements are held over, but a larger pro- 

 portion of equally important Middle Cambrian elements are intro- 

 duced, and new introductions must always outweigh holdovers. The 

 constitution of the Ptarmigania fauna emphasizes anew the close 

 relationship between the Lower and Middle Cambrian. As our 

 knowledge increases it becomes ever clearer that there is no diastrophic 

 break between Lower and Middle Cambrian, and the faunas likewise 

 show no great change. 



The close relationship to the Albertella fauna has been mentioned. 

 On the one hand such genera as Ponlsenia, Dolichomctopsis, Prosa- 

 canthoides, Kootenia, Hclcionella, and Wimanella relate the Ptarmi- 

 gania fauna to the upper Mount Whyte and Lower Cambrian faunas 

 in the Appalachian region. On the other hand Kochaspis, Kootenia, 

 and Clavaspidclla are more characteristic of early Middle Cambrian, 

 while such genera as Pagetia, Oryctocephahts, BatJiyitriscus, and 

 Olenoides are more characteristic of later Middle Cambrian. The 

 unique genera are, of course, left out of consideration, and the 

 brachiopods are of no assistance. 



Glossopleura is not in the Ptarmigania fauna at Two Mile Canyon. 

 It is found throughout the lower half of the Middle Cambrian quite 

 commonly and consequently can be expected in any of the faunas. 



Summing up present evidence, it seems that the Ptarmigania fauna 

 occurs in early Middle Cambrian beds, which are to be correlated 

 with some part of the Ptarmigan, Ophir, and Howell formations in 

 the west, and with the Rutledge of the Appalachians, and particularly 

 with the Cape Wood formation of northwest Greenland. At the 

 present stage of our studies the Ptarmigania fauna is most like that 

 of the Comet shale in the Pioche district, Nevada. 



