﻿2o Bulletin 20 98 



Evidence of the fauna. — The fauna of the Jefferson limestone as 

 known at present is a small one, numbering about 32 species. 

 Like many other western faunas it includes very few species 

 which are common to the standard sections east of the Mississippi. 

 Of the five species which are common to the well-known eastern 

 sections all except Atrypa reticularis are characteristic Devonian 

 species, a sufficient number to make evident the Devonian age of 

 the fauna. 



In looking for the equivalent of this fauna among western 

 Devonian faunas, the geographic proximity of the Ouray fauna 

 invites comparison of the two. Such comparison, however, 

 shows that the resemblance is slight and the differences are most 

 pronounced. Camarotcechia endlichi may be considered the 

 most characteristic species of the Ouray fauna, for it has been 

 found at practically every outcrop where that fauna has been 

 recognized from northern Colorado to southern New Mexico. 

 This species, although so abundant in the Ouray fauna, is entirely 

 unknown in the Jefferson limestone. On the other hand, species 

 which from their abundance in the Jefferson limestone may be 

 regarded as dominant species are absent from the Ouray fauna. 

 Three of the most abundant forms in the Jefferson limestone 

 fauna are Spirifer utahensis, Sp. engelmanni, and Martinia maia. 

 Neither of these three is known in the Ouray fauna. All three of 

 these species, however, are characteristic fossils of the Nevada 



near Philipsburg, Mont., in consequence of which the beds from which 

 they came were included by Mr. Weed in the Jefferson limestone. (U. S. 

 Geol. Survey, Ann. Rept. twentieth, pt. 3, 1900, p. 288). The fossils 

 examined comprised five species, two Rhynchonellas which were compared 

 with Camarotcechia sappho and C. congregata, and an external mold of a 

 pelecypod identified as Glyptodesma rectum? an indeterminable Aviculi- 

 pecten and a cyathophylloid coral. The two Rhynchonellas which had 

 the internal structure and configuration of Camarotcechia rather than of 

 Pugnax, were unlike any Pennsylvanian species known to me and afforded 

 some warrant for the age determination then given out. A reexamination 

 of this material, however, in connection with additional paleontologic and 

 stratigraphic data, leaves no doubt that the age is really Carboniferous, 

 probably Upper Carboniferous. The impression referred to Glyptodesma 

 rectum? almost certainly belongs to a rare species of Myalina related to or 

 perhaps identical with M. deltoida Gabb. — George H. Girty. 



