Notices of New Forms of the Genns Graptolilhns, and Allied 



Genera. 



[ From the Supplament to Vol. i, published in Vol. iii, Pal. N.York, p. 510 - 520.] 



GRAPTOLITHUS 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 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 distinctly 

 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, jn their mature condition, all present the peculia- 

 rity 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 pro- 

 cess 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, dis- 

 closes the remains of a minute transverse filament; and others show a fracture or 

 separation along the rachis between the two sets of branches, corresponding, 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 

 been able to discover any extension of these parts, or evidence of a third or fourth 

 main branch or stipe. Although it is not possible at the present time to determine 

 fully the mode of growth, and the original form of this species when entire, we are 

 nevertheless able to offer some additional information which may be of interest. 



In the minute forms which appear to be the young of this species, no lateral 

 branches are developed, while the centre or base is marked by a transverse bar 

 which extends almost equally on either side of the stipe or rachis. The accompany- 

 ing figures 1-4 are illustrations of this form, which are enlarged to twice the 

 natural size, fig. 1 presenting the animal in its earliest observed stage of develop- 

 ment. 



