UPPER CARBONIFEROUS 131 



is about 4,000 feet thick. The faunas of the two divisions of the 

 Guadalupian are closely related to one another. They are very 

 rich and varied, having already furnished over 325 species. The 

 Guadalupian fauna is peculiar. But few of its species are com- 

 mon to the other American faunas and some of its genera, such as 

 Richthofenia, Leptodus, Geyerella and Aulosteges, have not been noted 

 elsewhere in the western hemisphere. Even the more common genera 

 are in many cases represented by uncommon types. As an instance 

 may be mentioned the genus Composita (Seminula), which, by the 

 way, seems to be rather characteristic of our American faunas where 

 it is ever present and ever abundant. In the Guadalupian this 

 genus develops a bi-lobed species with a sinus on the dorsal as well 

 as on the ventral valve and a deeply emarginated anterior border. 



It is possible that the Guadalupian fauna may have an equivalent 

 in California in the Robinson formation, in which I have noted a 

 species of Leptodus, and a suggestion is contained in some forms from 

 Nevada, but aside from this the Guadalupian facies is known only in 

 a limited area in New Mexico and Texas. 



It remains to speak of still another western fauna having a pro- 

 nounced facies, a wide distribution, and a range through a consider- 

 able thickness of rocks. I mean the fauna of the so-called Permo- 

 Carboniferous of the Wasatch Mountains, and the Permian of Mr. 

 Walcott's Grand Canyon section. This fauna, which ranges also into 

 Wyoming and Idaho, comprises litde else than pelecypods, of which 

 Myalina and Aviculipecten are the most common types, the Pectinoids 

 being especially abundant and varied. It may tentatively be corre- 

 lated with the Guadalupian (Delaware Mountain division), athough 

 it presents but little resemblance to the Guadalupian fauna as at 

 present known. At least, it appears to occupy a corresponding 

 position in the section, resting upon strata which in the light of our 

 present knowledge are correlated with the Hueco formation. 



These western faunas are more easily correlated with those of 

 Europe, especially Russia, than with those much nearer geographic- 

 ally, in eastern North America. Indeed, the correspondence of our 

 western faunas with those of Russia is truly remarkable. The Russian 

 series consists, in ascending order, of the Mountain limestone, or 

 Produdus giganteus zone; the Moscovian, or " Lower Carboniferous;" 



