Genus Graptolithus. 160 



Instead of the narrow filiform mid-rib represented in the figures 

 and descriptions of the authors mentioned, these specimens pre- 

 sent a broad linear mid-rib 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 instances nearly half an inch in 

 length. The mid-rib 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 mid-rib is 

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

 they nevertheless present all the characteristics which they ex- 

 hibit in graptolites of other forms, in which the branches have 

 been compressed vertically to the direction of the serratures. 



In this view, the lateral leaf-like portions appear to be appen- 

 dages 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 mid-rib is strong and 

 broad, often prominent and distinctly serrate, the edges of the in- 

 terspaces 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 lateral parts* 

 This remarkable feature leads to the interference that this grapto- 

 lite was composed of four semi-elliptical parts joined at their 

 straight sides, and projecting rectangularly to each other, present- 

 ing 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. 



In another more elongate form, the specimens examined are ex- 

 tremely compressed, and I have not been able to detect serratures 

 in the axis, which however is sufficiently wide to admit of this 

 feature. 



For these remarkable forms, whether consisting of bilateral or 

 quadrilateral foliate expansions, or with two or four series of cell- 

 ules, I propose the name of Phyllogr^ptus, from their leaf-like 

 appearance when compressed in the slaty strata. 



It is easy to perceive how bodies formed as these are may pre- 

 sent different appearanct-s, dependant upon the line of separation 

 of the parts by the slaty lumince. When separated longitudinally 



