268 
PALAEONTOLOGY OF NEW-YORK. 
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. 
Joliaceus 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 frond. 
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.sp.). 
Pl. LXXIII. Figs. 1 a, b, 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 observed 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. 1 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 the partially altered and folded 
slates of the Hudson-river group near Albany. 
324. 5. GRAPTOLITHUS BICORNIS (n.sp.). 
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 the stipe, obtuse at the extremities; axis capillary ; base or radix bifurcate. 
This species is clearly distinct from either of the preceding, and easily identified by the 
