TRENTON CONGLOMERATE OF RYSEDORPH HILL 25 



pLECTORTHis Hall & Clarke 

 Plectorthis plicatella Hall 

 Orthis plicatella Hall. Pal. N. Y. 1847. 1:122 

 Several large specimens of this species were found in the 

 gray crystalline limestone pebbles. Hall reports the form as 

 very rare in the lower Trenton of Xew York, while in the west 

 it is common from the upper Trenton to the Lorraine beds. It 

 has lately been found to ascend into the upper Utica beds in the 

 vicinity of Albany. (Group 7) 



PLATYSTROPHIA Kiug 



Platystrophia biforata Schlotheim sp. 



Terebratulites biforatus Schlotheim. Petrefaaten- 

 kunde. 1820. p. 265 



With one exception all specimens of Platystrophia 

 biforata, which is quite common in the compact black lime- 

 stone pebbles, are only middle-sized, have rounded cardinal 

 angles and only five to six not very strongly developed plications 

 on either side of fold and sinus, while the usual number is from 

 12 to 16 plications on either side, and at least 12 in Trenton 

 specimens of the same size from ^ew York. As Winchell and 

 Schuchert^ state that the earliest individuals of this species, 

 which ranges from the Chazy to the Kiagara formation, are 

 small in size and have but few and simple cos-tae, characters 

 which also appear in the young individuals, the immature 

 characters of the specimens collected at Rysedorph hill point to 

 a rather early age for the black limestone. (Group 5) 



DALMANELLA Hall & Clarko 



Dalmanella testudinaria Dalman sp. 



Or this testudinaria Dalman. Kongl. Svenska. vet. 

 akad. Handl. for 1827. 1828. p. 115 



Dalmanella testudinaria is very common in the 



gray and black compact limestone pebbles of Rysedorph hill, 



Moordener hill and Schodack Landing. (Groups 5, 7) 



1 Geol. Minn. Pal. 1897. v. 3, pt 3, p. 456. 



