Silurian.] PALAONTOLOGY OF VICTORIA. { Graptolites. 
Puate L., Fras. 1, 2, 3, 4 
GRAPTOLITES (DIDYMOGRAPSUS) THUREAUI 
(McCoy). 
[Genus GRAPTOLITES (Liy.). (Class Zoophyta. Order Hydrozoa. Fam. Graptolitide.) 
Gen. Char.—Polypidom horny, elongate, compressed, with a slender solid axis along one 
edge, followed by a parallel common longitudinal canal, from which one close row of cells 
extends, each inclined upwards and outwards, and all terminating in separate apertures on the 
serrated edge opposite the solid axis. 
Sub-genera.—1, Graptolites (proper). Stem single and simple ; Upper and Lower Silurian. 
2, Didymograpsus (McCoy). Stems simple, but united in groups of two or more by the pointed 
uncelled lower end. Some of these have around horny dise connecting the non-celluliferous 
bases of the grouped stems ; Lower Silurian. Some writers divide the species into sub genera 
Tetragraptus, Loganograptus, &c., according to the number of stems conjoined, a character 
certainly not of generic value. ] : 
DescriptTion.—Radicle conical, minute, in the middle of a short straight funicle 
14 lines long, which bifurcates equally at each end, giving rise to the four equal main 
branches or stolons of the complete polypidom ; each branch about 1 inch long, bent 
recularly in zigzag angles of about 135°, alternately giving off at intervals of about 
1 line, on both sides from the salient angles, the regular, straight, simple stems, five 
or six in number on each side, and about 1 inch in length (more or less as they are 
nearer the base or the apex), each with a row of broad, acutely angular cell-denticles, 
seven in the space of 3 lines ; the upper edge of each cell slightly convex and nearly 
at right angeles with the back, and rather longer than the undivided portion, the lower 
edge two-thirds uncovered by the next cell, and making an angle of about 45° with 
the back ; from the point of one cell to the next about equal to the width from the 
same point to the back. The whole polypidom, of about forty stems, forms a slightly 
quadrate circle or rounded square about 2 inches in diameter. 
REFERENCE.—McOoy, Ann. and Mag. Nat. Hist. v. 18, p. 129 (1876). 
This species will not quite fit into any of the newly suggested 
genera of recent writers ; so I fall back for the present on my old 
genus Didymograpsus, with an extension which might make it 
include all compound Graptolites having more than one unbranched 
stem, with a single row of cells each, arising from an uncelluliferous 
connecting basal tube or radicle and funicle (including Logano- 
graptus, Dichograptus, &c.). 
I name this species after the discoverer, M. Thureau, of Sand- 
hurst, who first brought it under my notice, and who has presented 
two specimens (one nearly perfect) to the National Museum at 
Melbourne. The regular zigzag bendings of the four branches of 
the funicle, from which the stems arise, form an arrangement of 
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