45 



The axis projects slightly beyond the proximal end, and often to 

 a considerable distance beyond the distal end of the celluliferous 

 portion of the stipe. The stipe is narrow at the base, but expands 

 gradually until it attains the full width, which is about one-tenth of 

 an inch. The cellules are narrow and closely arranged, numbering 

 about twenty-eight in the space of an inch, and they terminate 

 abruptly at the distal end of the stipe (Fig. 15). 



The genus Climacograptus also comprises forms that have two 

 rows of cellules, but it differs from Diplographis prisiiniformis in 

 the shape of the cellules, which are so bent towards the distal end 

 of the stipe, that the outer position of each becomes parallel with 

 the axis ; the cell-mouth being sunk within the margin of the stipe, 

 and completely sheltered by the next cellule. 



Climacograptus atitennarius is a typical specimen of this genus. 

 It consists of a short double-celled stipe about an eighth of an inch 

 in width, having a strong axis, which often extends beyond the 

 distal end, as much as the entire length of the celluliferous portion 

 of the stipe ; it also projects slightly beyond the proximal end. 

 Moreover, the base of the stipe is furnished with two strong spines, 

 one on each side, diverging at an angle of about sixty degrees. 

 The cellules are bent upward, and their mouths depressed below 

 the margin of the stipe (Fig. 1 6). 



The vertical range of the genus Diplograptus extends from the 

 Skiddaw Slates, through the Llandeilo and Caradoc rocks ; and 

 Climacograptus ranges through the same strata into the Lower 

 Llandovery beds. 



Tetraprionidian Group. 



This group consists of forms having four rows of cellules, or 

 they may be described as four monoprionidian stipes placed back 

 to back, having an axis running through the centre, and projecting 

 slightly at the base. 



Phyllograptus typus is the most common of the Tetraprionidian 

 forms. The stipes are usually short and broad, the general shape 

 being an elongated oval. A strongly marked axis is always present. 



