THE MISSISSIPPI AN PERIOD 611 



The Waverly fauna. Contemporaneous with the evolution of 

 life in the Kinderhook and Osage seas, there was a rather more 

 provincial development east of the Cincinnati axis. There was 

 no impenetrable barrier between this tract and the sea farther west, 

 but, owing partly to the partial separation and more perhaps to 

 other physical conditions, the fauna east of the Cincinnati arch 

 was somewhat distinct from that west of it. 



The Waverly fauna was the direct descendant of the Devonian 

 faunas that had occupied the same ground, and had changed but 

 slowly, as the environment remained nearly constant. It was 

 modified by some immigration of the Kinderhook and Osage types, 

 and took on slowly a Mississippian aspect, while retaining many 

 Devonian characteristics. Its most prominent members were the 

 pelecypods, as might have been anticipated from the silty condi- 

 tions. Many of them were the same as the late Devonian of the 

 same region. Brachiopods were numerous and similar to those of 

 the Kinderhook and Osage faunas. The other forms were not very 

 different from those of the more open sea to the westward. 



The Waverly fauna was characterized negatively by the rarity 

 of both corals and crinoids, the apparent reason being their depend- 

 ence on clear seas. Locally, however, crinoids abounded. 



The Great Basin fauna. It will be recalled that the Great Basin 

 was a province by itself in the Devonian period, where a slow faunal 

 development of provincial aspect took place, modified slightly by 

 foreign contributions. The transition from the Devonian to the 

 Mississippian fauna seems to have been gradual, and effected 

 through the progressive evolution of some forms, the elimination 

 of others, and the immigration of a few from westerly sources, and 

 after the Osage epoch, perhaps from easterly sources as well. At 

 the close of the Osage epoch, the Basin fauna united with the 

 Osage fauna to form the Genevieve (St. Louis-Kaskaskia) fauna 

 of the interior. 



Previous to this union, one of the most salient distinctions be- 

 tween the Great Basin fauna and the Osage fauna was the rarity 

 of crinoids in the former.. Although the Osage sea stretched west- 

 ward to the mountains at least, and was prolific in crinoids, they 

 do not seem to have invaded the Great Basin sea, a fact which 



