Lower Silarian.] PALAEONTOLOGY OF VICTORIA. IGraptolites. 



Plate II., Fig. 1. 



GRAPTOLITES (DIDYMOGRAPSUS) QUADRIBRA- 

 CHIATUS (Hall sp.). 



[Genus GRAPTOLITES (Lin.). (Class Zoophyta. Order Hydrozoa. Fara. Graptolitids.) 



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 iu separate apertures on the 



serrated edge opposite the solid a.xis.] 



[Sub-genera. — 1. Graptolites (proper). Stem single and simple ; Upper and Lower 

 Silurian. — 2. Didymograpsus (McCoy). Stems simple, but united iu groups of two or more 

 by the pointed uncelled lower end. Some of these have a round horny disc, connecting the 

 non-celluliferous bases of the grouped stems ; Lower Silurian. Some wi'iters divide the 

 species into sub-genera Tetragraptus, Loganograptus, &c., according to the number of stems 

 conjoined, a character certainly not of generic value.] 



Descrtption. — Central stipe straight, rather less than 2 lines long and about \ 

 of a line wide, bifurcating at each end into 3 equal linear branches (4 in all), diverging 

 at about 95°, branches usually upwards of 1 J inches long (broken at ends), and after 

 ^ inch from the base, about 1 line wide to tip of denticles, for the remainder 

 of their length ; denticles varying in the same branch from 5 to 6 in 3 lines, 

 indented rather more than j the width of the branch near the base, and slightly less 

 at a distance from it; points moderately acute, and ver}' slightly recurved at the apex 

 (the lower edge filiformly produced in a few instances), the lower boundary line of 

 each cell reaching the inner edge of the tubular canal of the back at a point 

 coinciding with a line at right angles to the back, passing through the point of the 

 second lower cell; the upper edge of the cell denticles is sometimes convex, and 

 sometimes concave in the same branch, and is about § the length of the lower edge. 



Reference. — (Hall), Can. Org-. Rem., dec. 2, t. 5, figs. 1-5, p. 91. 



One specimen from (B" 29) Newliam shows clearly one of the 

 4 connected "branches bent back, exhibiting a length (imperfect at 

 the end) of Z\ inches ; the denticles 5 in 3 lines, and the width 

 very slightly exceeding 1 line ( Ig) ; the character of this part of the 

 branch so exactly resembles some straight fragments in the same 

 flags, broken at each end, but 8 inches long, that I feel inclined 

 to refer the latter to the present species. The branches in all the 

 specimens are nearly straight, but slightly curved with the con- 

 cavity usually on the denticulate side ; and this character is seen in 

 the large fragments mentioned, and separates them from all the 

 varieties of G. Ludensis and G. Sagittarius, as well as the greater 

 width of the branches and the more sunple form of the denticles, 

 which are never thickened and abruptly hooked as in these latter 

 species. 



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