No. 186.J 53 



These bodies, which usually appear upon the stone in the form of simple 

 leaf-like expansions, may possibly have been attached in groups to some 

 other support; but the form of some of them, and the character of the 

 projecting radicle at the base, indicates that we have the entire frond. 

 These forms furnish perhaps the best illustration of all the Graptolitide(X., 

 of the lesser development of the cells at the base, and their gradual ex- 

 pansion above until they reach the middle or upper part of the frond. Many 

 of them diminish from the centre upwards ; and rarely the cells are more 

 developed above the centre, reversing the usual form, and leaving the 

 narrower part at the base. 



The species of this genus approach in general form to G. ovatus of 

 Barrande and G. folium of Hisinger. They present, however, some 

 differences of character ; varying from broad-oval with the extremities 

 nearly equal, to elongate-oval or ovate, the apex usually the narrower, but 

 in a few instances the base is narrower than the apex. These forms are 

 sometimes extremely numerous in the shales, and present on a cursory 

 examination a general similarity to the leaves of large species of Neuro- 

 jpteris in the shales of the Coal measures. 



Instead of the narrow filiform midrib represented in the figures and de- 

 scriptions of the authors naentioned, these specimens present a broad linear 

 midrib continued from the apex to the base, and extended beyond the base 

 in a slender filiform radicle, usually of no great extent, but in some in- 

 stances nearly half an inch in length. The midrib is rarely smooth, varying 

 in width, with its margins not often strictly defined. In examining a great 

 number of individuals of one species, I have discovered that this midrib 

 is serrated ; and though for the most part the serratures are obscure, they 

 nevertheless present all the characteristics which they exhibit in graptolites 

 of other forms, in which the branches have been compressed vertically to 

 the direction of the serratures. 



In this view, the lateral leaflike portions appear to be appendages to the 

 central serrated portion ; but these are nevertheless denticulate on their 

 margins, and the intermediate spaces are well defined, as if admitting of no 

 communication by serratures or cellular openings with the centre. 



In another species the central axis or midrib is strong and broad, often 

 prominent and distinctly serrate ; the edges of the interspaces being all 

 broken off, as if the extremities had been left in the slate cleaved from the 

 surface : at the same time, the lateral portions are so well preserved as to 

 show distinct cellules upon each side. We have therefore three ranges of 

 cells visible, the central axis projecting at right angles to the two latei-al 

 parts. This remarkable feature leads to the inference that this graptolite 

 was composed of four semielliptical parts joined at their straight sides, 

 and projecting rectangularly to each other; presenting on each of the four 

 margins a series of serratures, which, penetrating towards the centre, were 

 all united in a common canal, and all sustained upon a .simple radicle. 



