GEOLOGY OF THE LOWER AMAZON REGION 733 



curta. Tropidoleptus carinatus is known in a single example from the 

 Oriskanian of Maryland; it is also abundant in the Lower Devonic 

 of Germany, and, as Williams has shown that this shell is also known 

 in the Chemung, it therefore has lost its diagnostic value as a marker 

 of the Hamilton formation. Vitulina pustulosa is thus far in eastern 

 North America a good Hamilton marker, but in South America it is 

 always found in faunas that have an older aspect. 



This Maecunl fauna has ninety-two species, and of these the 

 following six Oriskanian forms are known in it: (i) Rhipidomella 

 musculosa, (2) Leptostrophia perplana^ (3) Anoplia nucleata, (4) Am- 

 phigenia elongata curta ^ (5) Anoplotheca flabellites, and (6) Tropido- 

 leptus carinatus. Certainly numbers 1,3, and 5 are diagnostic of the 

 Oriskanian, and are usually regarded as guide fossils. Combining 

 these occurrences with the other facts mentioned above, it seems to 

 the writer that there cannot be any doubt that the Maecuru fauna 

 holds the horizon of the North American Oriskanian. If further 

 proof of this is required, the reader is referred to Katzer's Plates X, 

 XI, XII, and XV. On the other hand, the view of Clarke (who has 

 studied nearly the entire fauna by the specimens), while not exactly 

 that of the writer, is still not widely different (hardly one formation 

 apart). He states (5:91, 92) the following: 



The opinion expressed by Derby [6: i6q] and Rathbun that the Maecuru and 

 Erere groups bear about the same stratigraphical and paleontological relation 

 to each other as the Upper Helderberg group to the Hamilton, is supported by all 

 evidence now accessible. 



It is indeed probable that the Maecuru group embraces elements of faunas 

 that elsewhere precede those of the Upper Helderberg (Schoharie grit, Cornif- 

 erous limestone), a fact indicated by the earlier expression of the trilobitic ele- 

 ment and by the presence of certain molluscan species (Platyceras hariti, Anoplia 

 nucleata) of the same import. 



Notes on the fauna of the Erere formation. — Hartt (2:213) in 

 describing the Erere locality states : 



This fauna has an unmistakable Devonian facies, but it is diiificult to deter- 

 mine its exact equivalency. In some features, as for instance in Spirifer pedroana, 

 which closely resembles S. varicosa, the fauna recalls that of the Corniferous, 

 while in the occurrence of Tropidoleptus and Vitulina it approaches the Hamilton. 



Rathbun (3 : 260) in his first studies of the Erere brachiopods con- 

 cludes : 



