622 



NEW YORK STATE MUSEUM 



Tetragraptus shale of tlie Levis beds in Canada, noting in a description 

 of the same the presence of a central disk which had not been observed in 

 Australia. 



Description. The rhabdosome consists of two short monothecal branches 

 of the first order (" funicle ") growing from a relatively long, stout sicula 

 (2.2-2.7 mm in different specimens). The ''funicle" varies from 



2 . 3 to 3mm in length. It divides 

 by dichotomy at both ends into 

 two short branches of the sec- 

 rig. 37 Goniograptus thureaui McCoy. Fragment of oud Ordcr wLlch form an anei;le 

 a branch in which the coenosarca) canal and the proximal por- " 



tions of the thecae have become infiltrated with pyrite and the • i , ^„„ -| oAo „^^ -\AC\o 



successive gemmation of the thecae is well shown. Deep kill. Varying DetweeU ioU aUQ i4tU . 



These bifurcate again, forming 

 two branches, one of which grows out into an undivided denticulate branch, 

 while the other monothecal one bifurcates, producing a denticulate branch 

 on the opposite side. This process is repeated till four zigzag shaped, 

 principal stems are formed, reaching a length of 10 mm 

 and lying approximately in the diagonals of a rectangle, 

 forming two pairs of angles, the one at the end of 

 the " funicle " being about 75°, the other on both sides 

 of the same 105°. The denticulate branch forms an 

 angle of 45° with the stem and the last pair of suc- 

 ceeding denticulate branches form approximately a 

 right angle at their bases. The whole rhabdosome 

 expands in the form of a square with convex sides. 



Well preserved, mature specimens often possess a 

 chitinous disk which clasps the " funicle " and the 



principal branches to the base of the terminal denticulate branches. The 

 breadth of this alate extension has not been found to surpass 1 . 3 mm. 

 The diameter of the largest colonies was observed to be 110 mm. The 

 thecae are long and narrow, number 8 to 10 in 10 mm, overlap about one 

 half of their length ; their outer walls are slightly concave and are 

 inclined at about 30° to the axis of the branch in the distal parts ; their 



Fig, 38 Goniograptus 

 thureaui McCoy. Frag- 

 ment of branch enlarged. 

 Deep kill. x4.5 



