452 



NEW YORK STATE MUSEUM 



as Nautilus k e 1 1 o g g i , viz : Eurystomites k e 1 - 

 1 o g g i Whitfield ( sp. ) , E . rotundus Hyatt and E . v i r g i n i - 

 anus Hyatt. The first of these species has been redescribed by 

 Schroder, the other two by Hyatt. They are all three referred 

 to or can be said to constitute at present the genus Eurystomites,. 

 which according to Schroder has the following diagnostic char- 

 acters (translated). 



Shell completely coiled in a spiral. Aperture expanded, with a 

 simple hyponomic sinus. Sipho centriventral to ventral. 



Nautilus? c h a m p 1 a i n e n s i s was also referred by Schrod- 

 er to his genus Eurystomites, but has been brought by Hyatt [1894, 

 p. 435] together with Lituites seelyi Whitfield, another Fort 

 Cassin form, under Tarphyceras, while Lituites eatoni Whit- 

 field, which was referred by Schroder to Discoceras has been made 

 by Hyatt a member of his new genus Schroederoceras and Litu- 

 ites internestriatus Whitfield, a fourth Fort Cassin species,, 

 also a Discoceras according to Schroder, is considered by Hyatt a 

 typical Trocholites. 



Later [1897, p. 182] Professor Whitfield described still 

 another nautiliconic form from Fort Cassin, viz, N . p e f k i n s i . 

 This differs from Tarphyceras champlainense only in the 

 stronger development of the oblique undulations of the surface, but 

 agrees with it in all other important characters. - 



Of these genera of nautiliconic forms from New York and Ver- 

 mont, Eurystomites and Tarphyceras belong to the family Tar- 

 phyceratidae. This is characterized by the compressed oval section, 

 the venter of which is narrower than the dorsum ; the smooth or 

 nearly smooth shell and the empty and tubular siphuncle, which is 

 situated ventrad of the center. The genera Schroederoceras and 

 Trocholites are brought under the Trocholitidae, which are described 

 as follows : 



As a rule they have excessively broad volutions with reniform 

 section, and an impressed zone at a very early age; the siphuncle is 

 then ventrad of the center, but in the ephebic stage it is tubular and 

 dorsad of center. 



Since the original descriptions of W hitfield were partly emended 

 by Schroder and greatly enlarged by I [yatt's elaborate investigation 

 of the growth stages, based upon the large collection of the United 

 States National Museum, we can restrict ourselves here to an enum- 

 eration — with a few supplementary remarks — of the species which 

 have been identified in the material from the beds at Valconr. 



To facilitate the understanding of the somewhat complicated 

 generic references of these nautiliconic forms, we insert here two 

 synoptic tables. 



