Pernio -Carboniferous Ammonoids of the Glass Mountains 29 



may prove our conclusions to be wrong. Whatever may seem today 

 to be a type which was developed in a certain locality, tomorrow may 

 prove to be much more plentiful in a far distant locality. The modern 

 studies about the ammonites of the Mesozoic seem to demonstrate that 

 most of the genera, subgenera and even groups of species occur all 

 over the earth, at least during the period before the Upper Cretaceous ; 

 that they succeed each other in one region in the same manner as in 

 the other; and that only very few types developed locally. I do not 

 doubt that similar conditions existed in the Permian, the first forma- 

 tion where ammonoids begin to occur very frequently. 



If we compare the genera, subgenera and groups of species which 

 occur both in the Artinsk and in the Sosio beds, we find that there is 

 really a great similarity between the two faunas. The genera, etc., 

 which occur in both faunas are: Parapronorites, Medlicottia, Pro- 

 pinacoceras, Daraelites, Gastrioceras (group of G. Zitteli), Agathi- 

 ceras, Adrianites, Popanoceras, Stacheoceras, and perhaps Thalasso- 

 ceras, Paraceltites and Sicanites. Part of these genera are not of great 

 importance as they occur also in younger or older formations. Med- 

 licottia, for example, occurs certainly in different parts of the Permian; 

 Gastrioceras, Agathiceras and Stacheoceras (in the wider sense) are 

 even found in the Carboniferous. But Parapronorites, Propinacoceras, 

 Daraelites, Adrianites, Popanoceras, Thalassoceras, Paraceltites, and 

 Sicanites certainly appear to be limited to the lower part of the Per- 

 mian, where also the typical Medlicottia and Stacheoceras seem to have 

 attained their greatest development. The occurrence of these types in 

 both faunas tends to prove that the difference in age must be compara- 

 tively small, but that such a difference exists is proved by the oc- 

 currence of genera in the Artinsk which are generally of an older type, 

 and of others in the Sosio beds which belong to a younger type. We 

 shall discuss these particularities here a little more fully. 



In the Artinsk we find Pronorites, a genus which is most frequent 

 in the Carboniferous, and which is entirely missing in the Sosio beds. 

 Parapronorites which is nearly related to Pronorites, but shows a 

 higher developed suture, is very frequent in the Artinsk (nine species) 

 while in the Sosio beds it is represented by only one species. On the 

 other hand, Propinacoceras, which has perhaps a little more highly 

 developed suture than Parapronorites, is represented by three species 



