534 PEOCEEDINGS OF THE aEOLOGIOAL SOCIETY. [June 17, 



G, millipeda, M'Coy, Pal. Foss. pi. 1. B. fig. 6. 



Bastrites triangulatus, Harkness, Quart. Journ. Geol. Soc. vol. 

 vii. pi. 1. figs. 3 a-d. 



G. Clintonensis, Hall, Pal. N. York, vol. ii. p], 17. A. figs. 1 a-i, 



G. convolutus, Carruthers, Geol. Mag. vol. v. pi. 5. fig. 1. 

 No Graptolite, probably, is more protean in its form and presents 

 greater variations than does G. Sedgiuichii, Portl. Many of these 

 differences are, doubtless, due to the mode of preservation, or to the 

 age of the individual ; and others may possibly be of sexual value ; 

 but two varieties at any rate appear to be sufficiently well defined 

 to warrant us in giving them distinct names. "V^Tiilst some of the 

 forms under which G. SedgwicJcii appears approach closely to G. 

 lobiferus, M'Coy, others, again, make an approximation to G. Nilssoni, 

 Earr., whilst a third group shows a tendency to approach the genus 

 Rastrites. At the same time all the varieties graduate into one 

 another by a series of closely connected forms, so that only the 

 typical examples of each admit of being accurately placed. Further, 

 three species (viz. G, convolutus, His., G. proteus, Barr., and G. 

 millipeda, M^Coy) have been founded upon the slender curved base 

 of G. SedgwicJcii; and a fourth, G, spiralis, Gein., has been formed 

 from specimens of the same, in which the entire frond is rolled up 

 into a spiral, the coils of which lie in one plane. It will be evident, 

 then, that the examination of G. SedgwicJcii, and the discrimination 

 of its various forms, is beset with unusual difficulty, and that spe- 

 cimens will be constantly presenting themselves which it will be 

 impossible to assign with certainty to any recognized variety. 



The ordinary form of G. SedgwicJcii, as described by Portlock, and 

 as figured by M'Coy, consists of a simple monoprionidian stipe of 

 considerable but unknown length. The breadth of the adult por- 

 tion of the stipe from the solid axis to the cell -mouths is from one 

 to two lines. The axis is capillary ; and the common canal is broad 

 and conspicuous, sometimes attaining a width of nearly -^ of an 

 inch. The cellules are long, slender, and pointed, their superior 

 margins slightly convex and having a general direction at right 

 angles to the axis, their infferior margins more extensively curved, 

 the inner or basal portion being sharply inclined to the axis, whilst 

 the outer half is nearly horizontal. Each cellule, therefore, is 

 somewhat curved as a whole, and is of a triangular shape, the base 

 resting upon the common canal, and the cell-aperture being at the 

 apex. The cellules are from 20 to 24 in the space of an inch, their 

 general inclination being slightly upwards, or nearly at right angles 

 to the axis. Sometimes the cellules are curved to a greater extent, 

 and the cell-mouth points partially downwards ; but this is a distinc- 

 tion of trivial value, and depends probably upon the mode of pre- 

 servation of the specimen. 



Other examples (PI. XX. fig. 28), whilst presenting aU the charac- 

 ters of the above, have the stipe curved into a spiral, all the volu- 

 tions of which lie in the same plane, thus coming to present the 

 form described by Geinitz under the name of G. spiralis (loc. cit.) 

 In these inrolled specimens it is seen that G. SedgivicMi commences 



