622 NEW YORK STATE MUSEUM 



Tetragraptus shale of the 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, i^gment of oud Order which form an angle 



a branch in which tlie coenosarcal canal and the proximal por- ^ 



tions of the thecae have become inflltmted with pyrite and the  ^ i,„j. „„„ i oAo „„A -i At\o 



successive gemmation of the thecae is well shown. Deep kill. Varying OetWeeU loU anu i4U . 



X5.25 J ^ 



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. Fig. 38 ooniograptua 



thureaul McCoy. Frag- 

 Well preserved, mature specimens often possess a o^p k?u. ^^Is"^ enlarged. 



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 



