510 NEW YORK STATE MUSEUM 



ences that the Champlain and Newfoundland basins have the greatest 

 number of genera in common ; further, that a considerable number 

 of the genera characteristic of these basins is present in the subse- 

 quent formations in the Mississippian sea and that finally from the 

 extra-American basins the Baltic basin appears to have a greater 

 number of genera in common with the American basin than either 

 the Atlantic or Bohemian-Mediterranean basins. On the whole these 

 inferences are verified by an analysis of the separate genera in regard 

 to their more or less restricted distribution and relative importance 

 for paleogeographic investigations. 



The genera which we here have in mind as being of more re- 

 stricted distribution on account of the aberrant or specialized char- 

 acter of their component species are : Nanno, Piloceras, Gonio- 

 ceras and Bathmoceras. The genus Nanno has been erected by 

 Clarke for a species from the Black river group (Ctenodonta bed) 

 of Minnesota. The principal diagnostic character of the genus 

 was seen in the presence of a large preseptal cone or nepionic 

 bulb. Holm possessing several species of lower Siluric cephalopods 

 with like nepionic bulbs, referred them also to Clarke's genus. 

 Hyatt, however, subsequently restricted the genus to forms, 

 which like the species from Minnesota, develop but a few endosipho- 

 sheaths and have the siphuncle in absolute contact with the external 

 wall. Thus determined the genus became again restricted to one 

 species. If now the form from the Chazy of New York, which in 

 the present paper, is, as we believe, on good ground referred to 

 Nanno, is correctly placed, we have in the Champlain basin an 

 earlier representative of the genus present in Trenton time in the 

 Mississippian sea. On the other hand, the genus Suecoceras Holm, 

 with an apical structure similar to that of Nanno, is represented, ac- 

 cording to its author, by six species from the Lower Siluric of the 

 Baltic basin and one from the Champlain basin. 



The characters of the genus Gonioceras are so striking that it 

 can not fail to be readily recognized wherever it is present. The 

 first species of this genus, G. anceps, was found in the Black 

 river formation at Watertown, near the outlet of Lake Ontario. It 

 occurs also in the Black river beds of Canada, and has been described 

 by Clarke from the Lowville limestone (Stones river group) of 

 Wisconsin and Minnesota, and is also recorded [in correlation table 

 of Paleontology of Minnesota] from the same formation in Ten- 

 nessee. Another species, G. occidentale, has been described 

 bv Hall from Wisconsin, where it is also found in the Stones river 



