702 NEW TORK STATE MUSEUM 



arranged alternating but in pairs This genus has not been recognized by 

 Roemer and Freeh in the Lethaea palaeozolca, but has been united with Coe- 

 nograptus. But, if the observation of the paired arrangement of the branches 

 is correct, the mode of bifurcation must be essentially different from that in 

 Coenograptus, Pterograptus etc. In fact, there is no other graptolite known 

 to the writer in which a paired arrangement of side branches occurs. 



All the other genera of the coenograptids (excluding Amphigraptus) 

 appear much later than Sigmagraptus. 



The stem or principal branch consists of thecae in exactly the same man- 

 ner as that of Pterograptus and Coenograptus, i. e. each internode between 

 two side branches is formed by one theca. 



Grenotype : Sigmagraptus p r a e c u r s o r sp, nov. 



Sigmagraptus praecursor sp. nov\ 



Plate 5, figure 13 



Coenograptid gen. nov. et sp. nov. Ruedemanii. N. Y. State Paleontol. An. Eep't. 

 1902. p.566 



The graceful slender branches of this species occur quite often in grapto- 

 lite bed 3 of the Deep kill section. As, however, they are usually mingled in 



an intricate manner with specimens 

 ^^^^^^^^^^^^^^^^^■^ of Groniograptus and other ramifying 



Fig. 93 Sigmagraptus praecursor sp. nov. SpCcieS, it is difficult tO obsCrvC pei'fcct 

 Part of branch. Deep kill, x 7 ^ ■*- 



organisms. The example figured was 

 found on a slab unobscured by other graptolites. 



Desci'iption. Rhabdosome consisting of two principal stems, which 

 together form a sigmoid curve. From these originate in regular intervals 

 long, straight, filiform side branches, only . 3 mm wide and which normally 

 form angles of 90° with the principal branches. The latter have been seen 

 to attain together a length of 40 mm, the side branches one cf 20 mm. The 

 sicula has not been found sufficiently well preserved for exact measurement ; 

 from it branch two primary thecae, with a length of 1 . 4 mm each, which form 

 a horizontal central bar. The internodes between the branches consist of one 



