GRAPTOLITES OF NEW VORK, PART 2 



403 



e— 



theca. It is true, Wiman states in the same publication | 1895, P-37] tna * 

 he also observed in Diplogr. uplandicus a rather distally beginning 



septum ; hut it is not apparent whether this is not an incomplete septum 

 such as Tornquist observed in Cephalogr. cometa resulting from a 

 narrow fold of the ohverse periderm ; and when we 

 examine the drawing's and species available of both 

 genera, Diplograptus and Climacograptus, it becomes 

 apparent that in Climacograptus a sutural groove is 

 always present and always begins near the sicular end, 

 allowing but a short " biserial chamber," while in Diplo- 

 graptus the lateral faces are nearly always smooth on both 

 the obverse and reverse sides, or at least on the latter, 

 indicating the absence of a complete longitudinal septum 

 or the presence of only a fold of the periderm on the 

 obverse side without a division of the rhabdosome into 

 two uniserial chambers. 



In forms like C . p u t i 1 1 u s where the double geni- 

 culation of the thecae and the apertural excavations are 

 still so little developed that a reference to Diplograp- 

 tus is possible, the presence of a distinct septal suture 

 [see fig. 370] beginning near the sicular end, is an argu- 

 ment for a closer relationship to Climacograptus and I 

 have therefore placed it with that genus. 



If we wish to arrive at an understanding of the 

 phylogenetic bearing of the relative development of the 353 



biserial and uniserial chambers, we shall have to resort, tu F s lg ku 5 c 3 ke C r I s , unu sH r o a im. 



Reverse view, x 32. Copy 



as in the case of the form of the theca of Climacograptus, fromWiman 

 to the Leptograptidae, in which, according to the important observation of 

 the British monographers, two crossing canals are present instead of the 

 one of the other Axonolipa. That means that here two pairs of alternating 

 thecae are developed, before the rhabdosome divides into two uniserial 

 chambers. Taking for granted the derivation of Climacograptus from 



c— 



