Permo-Carboniferous Ammonoids of the Glass Mountains 31 



even belong to a less highly developed precursor of that genus. (Pro- 

 thalassoceras. ) 



The occurrence of Paraceltites in the Artinsk is extremely doubtful, 

 while this genus is represented by four species in the Sosio beds. This 

 is important in so far as the sculpture of the genus is very similar to 

 that of the real ammonites, while the suture is somewhat archaic. 



The genus Daraelites was first described from the Sosio beds where 

 it occurs in only one species, represented by numerous specimens. An- 

 other and seemingly rather rare species has been described from the 

 Russian Artinsk by Tchernow. The genus has apparently a wider 

 range in age than has been thought. It occurs in our lowermost Per- 

 mo-Carboniferous of the Glass Mountains, Texas, although in only 

 two specimens. There it is represented by a new species which differs 

 from those of the Artinsk and the Sosio beds by the broad first lateral 

 lobe. Another species is known to occur in the Permo-Carboniferous 

 of St. Girons in the Pyrenees. 



A very interesting feature is the occurrence of Medlicottia in both 

 the Sosio limestone and the Artinsk sandstone. In the latter beds the 

 genus is represented by at least one species, while the Sosio beds contain 

 four species different from those of the Artinsk. Karpinsky had 

 thought that M. Orbignyana was possibly identical with M. Traiit- 

 scholdi Gemm., or that this latter one only represented a variety of 

 the Russian form ; but Noetling has already indicated a number of dif- 

 ferences in the sutural line and we may add that the form of the ex- 

 ternal saddle and of the adventive lobe A is very different in both 

 forms, and that also the lateral lobes have an evidently very different 

 outline. This is especially evident when we compare Gemmellaro's 

 figure with that of nearly the same size of M. Orbignyana given by 

 Karpinsky on his plate II, fig. 1, g, h and k. It seems also that the 

 furrow on the ventral part is much wider in M. Trautscholdi than in 

 the Russian form. 



Noetling has tried to determine the age of certain beds through the 

 development of the sutural line of Medlicottia. He supposes that the 

 geologically older species have a smaller number of auxiliary lobes and 

 also of rudimentary lobes on the external saddle than the younger 

 ones ; that the adventive lobe A is shallower in the older species than in 

 the younger ones, etc. But he supposed also that the cephalopod-bear- 



