266 PAUBONTOLOOY OF NEW-YOKK. 



this central axis is still preserved, extending beyond the other parts of the fossil. It expands 

 gradually, from what appears to be the base, upwards for some distance, but rarely exceeds 

 a single line in width. The serratures are usually acute, but sometimes obtuse. 



The aspect of this fossil is very variable, depending in some degree upon the nature of 

 the mass in which it is imbedded ; and it is not easy to determine what shall constitute 

 specific characters in bodies so obscure as these, and of which we have but fragments. In 

 the more calcareous portions of the rock they preserve a considerable thickness, but in the 

 thinly laminated shales they form a mere carbonaceous film upon the surface. 



I have given figures of this species from various localities, and in slates of slightly 

 different character, in order to present a faithful illustration of its usual form. 



Fig. 1 a. A fragrmen' of arenaceous slate, from the Hudson-river group at Turin, preserving the bases 



of several specimens. 

 Fig. I b. A portion of the same magnified. 

 Fig. 1 e. A magnified fragment of the same species on the opposite side of this specimen, showing 



obtuse serratures. 

 Fig. 1 d. A specimen of the same species, from the black slate of Oxtango creek, south of Fort-Plain. 

 Fig. 1 e. A magnified portion of the same. 



Fig. 1 / A fragment of the same species, from the olive slates of the Hudson-river group, at Loraine. 

 Fig. 1 g. The same magnified, showing the obtuse termination of the teeth. 

 Fig. 1 A. A specimen from the olive slate in Lewis county. 

 Fig. 1 i. A magnified portion of the same. 



Fig. 1 Jt A narrow and somewhat more finely serrated specimen, from the Utica slate. 

 Fig. 1 I. The same magnified. 



Fig. 1 «. A small specimen, showing the axis extending beyond the serrate portion in both directions. 

 Fig. 1 «. The same magnified. 



Fig. 1 0. A fragment of the same, from the black slates of the Hudson-river group near Albany. 

 Fig. 1 p. A magnified portion of the same, showing the acute teeth near the base, and the broader 



obtuse ones above. 



All these specimens clearly belong to the same species, and the slight variations are due 



to accidental causes, or to differences observable in different parts of the same specimen, as 



is shown in some degree in the magnified portion 1 p. 

 Fig. 1 r. This sjjecimen resembles G.foliaceus of Murchison, and differs slightly from the preceding 



in the short mucronatc points of the teeth, shown in the magnified portion 1 s. In other 



respects it is similar. 



Position and locality. This species occurs in the Utica slate, and in the olive slates of the 

 Hudson-river group, often very abundantly, and is widely distributed. It is found in great 

 numbers in the black slate near the city of Hudson; at Stuyvesant, Columbia county ; 

 near Albany, Ballston and Baker's falls, in a similar slate ; in the Utica slate near Fort-Plain, 

 and at Herkimer, as well as other places in the Mohawk valley ; in the olive or greenish 

 slates of the Hudson-river group at Loraine, Jefferson county, and at Turin in Lewis 

 county, M well as several other localities in that part of the State. 



