SIO PAI.yEONTOLOGY OF NEW-YORK. 



iiraptolitlius gracilis. 



This species was first described in the Palaeontology of New- York, 

 Vol. 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 ofier 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 



