510 
PALEONTOLOGY OF NEW-YORK. 
Graptolithus gracilis. 
This species was first described in the Palaeontology of New-York, 
Yol. i, p. 274. Its usual form is that of a slender sinuous stipe or rachis, 
from one side of which are diverging branches which are serrated on one 
margin only. I have lately farther illustrated this species in the Regents’ 
Report upon the State Collections of Natural History. A subsequent 
examination of the specimens from the Normans-kill, near Albany, has 
shown some modifications of its form and mode of occurrence, not before 
observed, which make it necessary to offer some farther illustrations in 
this place. The species may be described as follows : 
Frond bipartite (or quadripartite ?), consisting of two principal stipes : 
stipes diverging from a point of attachment, and ascending more or 
less vertically; slightly curved in the young state, and more curved in 
older forms. Branches originating on the outer or lower side of the 
rachis; the first ones diverging almost rectangularly, while the later 
ones are more ascending, as large at their origin as the rachis, and 
becoming wider in their extension. Young branches thickened and 
succulent with the serratures obscure, becoming flattened and distinct¬ 
ly serrate in the older forms. In the full-grown specimens, the extremity 
of the stipe beyond the origin of the last branches is serrate. 
The specimens of this species, in their mature condition, all present the pecu¬ 
liarity of having a slender sinuous rachis, approaching in form the letter S, from 
which the branchlets diverge always on the convex side of the curve, so that 
ordinarily one half the branchlets proceed in one direction and the other half in 
the opposite direction. In the young specimens, there is a distinct appearance of 
a slender process or radicle from which the stipes diverge; and a more critical 
examination of some of the specimens having the S form, since this fact has been 
ascertained, discloses the remains of a minute transverse filament; and others show 
a fracture or separation along the rachis between the two sets of branches, cor¬ 
responding, as I had before suggested, with the centre or point of origin of the 
animal body. 
It is barely possible that this apparent central radicle may be the remains of two 
other stipes, corresponding to the two usually preserved; but we have not thus far 
