2o8 University of Texas Bulletin 



bate saddles as are most of the Sicilian species and M. primas Waag. 

 of India. 



Our two lowest horizons, i and 2, probably correspond to some part 

 of the Hess limestone in which no larger fauna of ammonoids has yet 

 been found. 



If we now extend our comparisons to strata of the old world, we find 

 for the first time distinct signs of relationship between a horizon of 

 Texas and the cephalopod-bearing sandstone of the Artinsk. In our 

 horizon i we found a Medlicottia which is nearly related to M. artien- 

 sis; in our horizons 2 and 3 we see a Medlicottia very similar to Medli- 

 cottia Orbignyana. In horizon i we also found a Stacheoceras nearly 

 related to St. Ronianowskyi,, while horizon 2 contains a Stacheoceras 

 with a much higher developed suture showing a great number of 

 auxiliary lobes and saddles. These forms begin to develop in the ceph- 

 alopod-bearing sandstone of the Artinsk, but are much more fre- 

 quent in the younger Sosio limestone of Sicily, and in the correspond- 

 ing Word formation of Trans-Pecos Texas. 



The Medlicottia in horizon 3 is so similar to M. Orbignyana that one 

 is nearly inclined to unite them in one species. 



All this induces us to regard our horizons i to 3 as more or less 

 corresponding in age to the cephalopod-bearing sandstone of the 

 Artinsk. This is entirely in accordance with what we have found in 

 the Trans-Pecos region. There we considered that the rocks contain- 

 ing Prothalassoceras are probably the equivalent of the Artinsk, while 

 the underlying horizon with Uddenites is certainly older than the 

 Artinsk, and may correspond to the period of erosion preceding it. 



But we must not forget to mention that in the Artinsk one form is 

 missing which in Texas is the most frequent one. I refer to Perrinites. 

 No species belonging to the Cyclolobinae has been found in the Russian 

 Artinsk; the first forms belonging to this group were discovered in 

 the Sicilian Sosio limestone, certainly a little younger than the Rus- 

 sian strata. But it seems that as yet Perrinites. has to be considered 

 as a local Texan branch of the Cyclolobinae, and J. Perrin Smith has 

 first advanced the theory that this branch developed from the American 

 genus Shumardites, a theory which has been proven right in the 

 present paper. It might thus be possible that the tribe of Perrinites 

 developed in America and from there migrated to the oceans of the 



