24 NEW YORK STATE MUSEUM 



Among the Russian forms is figured a pedicle valve with 

 depressed umbo and very convex pallia! region, which is quite 

 similar to our form. Taking all these facts into account, it 

 appears that the internal characters will hardly furnish any 

 points of difference between the forms, and that, when the gen- 

 eral form and the exterior are compared, the Trenton form com- 

 bines the cardinal extremities of the British with the striated 

 surface of the Russian species. 



triplecia Hall 

 Tripleeia nucleus Hall 

 Atrypa nucleus Hall. Pal. N. Y. 1847. 1 :138 

 A small Triplecia, evidently identical with Triplecia 

 nucleus Hall, was found to be common in the gray crystal- 

 line limestone pebbles of the conglomerate; a few .specimens 

 were also obtained from the compact reddish limestone with 

 ostracodes. Triplecia nucleus; has thus far been found 

 only in the middle Trenton of New York. (Groups 6, 7) 



orthis Dalman 

 Grthis tricenaria Conrad. Acad. mat. sci. Phil. Proc. 1843. 1:333 



Orthis tricenaria occurs quite frequently in typical 

 specimens of somewhat smaller size than those from the western 

 side of the Adirondacks, in the gray crystalline and compact 

 black limestone pebbles and in the cement. Its similarity to the 

 Chazy form, Orthis cos talis, together with the occurrence 

 of numerous cranidia and pygidia of Ampyx and Remopleurides 

 in the compact black limestone was at the first collecting quite 

 suggestive of the Chazy age of the compact black limestone peb- 

 bles; a suggestion, however, which the common occurrence of 

 typical Trenton fossils in the same pebbles proved to be mislead- 

 ing. (Cement and groups 5, 6) 



Orthis tricenaria is reported by Hall from the lower 

 Trenton of Middle ville; in the west it ranges from the Stones 

 river (Lowville) beds through the Black river beds into the Tren- 

 ton. Dr White did not locate it in the Trenton and Rathbone 

 brook sections. 



