268 PALEONTOLOGY OF NEW-YOKK. 



Still further east in the town of Chatham, where the slates are more altered, the Grapto- 

 lites present a greater approximation to those of Hoosick. After examining great numbers 

 of specimens from numerous localities, I am disposed to believe that the G. pristis, G. 

 foliaceus and G. folium, as well as the one here indicated, may all prove identical, the 

 differences being due to the greater or less degree of lamination in the shale, and the 

 preservation of different parts of the fiond. 



Position and locality. This variety, in its extreme character, is known only in the roofing 

 slate of Hoosick, in Rensselaer county, which overlies the partially metamorphic Trenton 

 limestone. Approximating forms occur at Baker's falls, on the Hudson ; at the city of 

 Hudson, and at Chatham in Rensselaer county. 



323. 4. GRAPTOLITHUS MUCRONATUS (n. 57;.). 



Pl. LXXIII. Figs. 1 a, A, c,d. 



Linear, compressed to a thin film ; axis capillary, serrated on both sides ; teeth with 

 mucronate tips. 



The serratures are slightly more distant than in G. pristis, and always mucronate. This 

 character has been oliserved in several small fragments, which are very closely pressed in 

 the thinly laminated slates. It is scarcely possible to conceive that the G. pristis assumes 

 this character in some of its parts, and it cannot be due to pressure, since both forms 

 occur together in the slates. 



Fig. 1 a. Two fragments of this species. 

 Fig. I b. A portion of one enlarged. 



Fig. 1 c, d. Fragments of the same species, one of them much contracted, and both preserving extremely 

 mucronate teeth. 



Position and locality. This species has been seen only in tlic partially altered and folded 

 slates of the Hudson-river group near Albany. • 



324. 5. GRAPTOLITHUS BICORNIS (m. 5;).). 



Pl. LXXIII. Figs. 2 a - s. 



Stipe linear, elongated, compressed, narrow, gradually widening from the base upwards; 

 width one line or less ; serrated on both sides; serratures slightly oblique ; teeth about half 

 the width of tlie stipe, obtuse at the extremities; axis capillary ; base or radix bifurcate. 



This species is clearly distinct from either of tlie preceding, and easily identified by the 



