130 CARBONIFEROUS AMMONOIDS OF AMERICA. 



of the Arcfestidse older than the Permian. Karpinsky" has shown that 

 Medlkottia came directly from Pronorifes, which is known in the Lower 

 Carboniferous in both Europe and America. Thus the whole argument 

 for a Permian migration from the Southern to the Northern Hemisphere 

 falls to the ground. 



The Paleozoic Cyclolobidfe are known at present onlj- in Texas, ihe 

 Mediterranean region, and in India. The Paleozoic Pojjanoceratidae are 

 known in these regions (with the exception of India), in the Ural 

 Mountains in Russia, and one form, Agathiceras f micromphalum Morris, has 

 been described from the Permian of Australia. But since both stocks 

 appear in the Coal Measures of America, and since their ancestor, Paralegoc- 

 eras, is known, in America, even in the Lower Carboniferous, both Cyclo- 

 lobidse and Popanoceratida^ probably originated in the American waters 

 and reached the rest of the world by migration at a later date. Their 

 differences of distribution do not, therefore, argue for climatic differences, 

 but rather for greater hardihood of the Popanoceratidae, which is borne out 

 by the fact not only that they migrated as far from their point of origin as 

 Russia on the one side and Australia on the other, but also that they 

 persisted with but little change as late as the Middle Trias. 



Family POPANOCERATIDAE. 



Genus Agathiceras Gemmellaro. 



To the writer it seems wiser to keep Agathiceras separate from Adri- 

 anites, because the former is a more primitive type, even though there 

 should be a perfect gradation between the two groups. Two American 

 species of ScMstoceras have been placed under Agathiceras; but those 

 species differ from the type in having an extra pair of lateral lobes, and in 

 not possessing the unusually strong development of the spiral lines, so 

 characteristic of all species of Agathiceras. Another characteristic worth 

 noting is that in Schistoceras the lobes and saddles are long, pointed, and 

 tongue-shaped, while in Agathiceras they are short and spatulate. 



"Ammoneen der Artinsk-Stufe, p. 86. 



