56 



BRITISH GRAPTOLITES. 



series, a reclined series, a dependent series, and, if we include the genus Fhyllo- 

 (jrapius, a scandent series. 



The genus Phyllogrnptiis, which is chai^acterised by the possession of four stipes 

 of the type of those of TelrmjrapUis, but conjoined by their dorsal margins, has 

 hitherto been regarded as a distinct genus, and by some even as the type of a distinct 

 family. Recent discoveries, however, have shown a practically complete gradation, 

 l)otli in the mode of development and in structure, between Phijllogvaptus and 

 Tcfnujrapfvs. In this work we retain Phi/llotjraptKS as a genus, on account of its 

 cliaracteristic habit — which is that of a Diplograptus, — but we group it as a member 

 of the family of the Dichograptidae (see postea), and we leave to future research 

 the possible demonstration that it is more naturally classed as a scandent Tetra- 

 graptid. 



The species here included in the horizontal, dependent, and reclined serial groups 

 of Tetvagraptus are as follows : 



Horizontal Series.— Group I. 



Dependent Series.— Gkouj' II. 



Giiour III. 



Reclined Series.— Guoir IV. 



Giioup V. 



Type T. quadribrachlatvs. 



T. quadrihracltiatns. 



T. crucifer. 



T. Headi. 



T. Amii. 

 Type T. fruticosiis. 



T. fraiicosus. 

 Type T. pendens. 



T. pendens. 



T. Postlothivaltu. 

 Type T. serra. 



T. serra. 



T. reclinatus. 

 Type T. Blgshyi. 



T. Bigshiji. 



HoKizoNTAL Series. 



Tetragrapti with t\V(j pairs of approximately straight and hori/>untal main 

 stipes, which make an angle of divergence of 180° with the line of the nema. 



Grou]) 1.— Type T. (jnadrihrachhttiis. 



Tetragra})li in which the main stipes are spread out in a horizontal plane; 

 they are commonly several centimetres in length. Their thecic are inclined at 

 high angles, and are in contact for the greater part of their length. 



