TROPIDOLEPTUS CARINATUS IN CHEMUNG FAUNA 353 



When it is recalled that the geographic range of this species 

 in the eastern United States during the Hamilton extended from 

 the Hudson River and the eastern part of the Allegheny Mountains 

 to Michigan, Indiana, and southwestern Illinois, it will be seen 

 that its east-west distribution was reduced during Portage time 

 to a very small fraction of that which it enjoyed during Hamilton 

 time. Our present knowledge of its occurrence in the Chemung 

 indicates that only a very small part of its east-west Hamilton 

 range was regained during the Chemung. The north-south 

 distribution of the species in the Allegheny region did not, however, 



Eastern New York 

 Central New York (Chenango Valley) 



Chemung <-.-.,. , , 



formation < S P lnfer d'S|unctus faun 



formation i Buchiola retrostriata fauna 



Tully .limestone 



Fig. i. — A diagrammatic east- west cross-section of the Middle and Upper Devo- 

 nian of southern New York showing the relations of Tropidoleptus carinatus to the 

 western faunas during Portage and Chemung time. Total thickness of the section is 

 about 2,700 feet. 



differ greatly during the Portage and Chemung epochs from what 

 it had been during the Hamilton. In this direction it appears 

 to have extended its range slightly in Chemung time beyond what 

 it had been during Hamilton time. During Portage time the 

 species was confined to a sublittoral belt, narrow but long, which 

 reached south into Virginia along the eastern shore of the Appa- 

 lachian sea. From the limits of this coastwise belt of the sea the 

 more favorable conditions of environment which accompanied 

 the initiation of Chemung sedimentation encouraged the migration 

 of its colonies westward into the areas where we now find them 

 in the Chemung of New York and Virginia. These colonies 



