Silurian.) PALAONTOLOGY OF VICTORIA. [ Graptolites, 
Prats XX., Fias. 3-5. 
GRAPTOLITES (DIDYMOGRAPSUS) CADUCEUS (Sattrr), 
DescrrpTion.—Radicle filiform, extremely slender, straight, and often 9 lines 
long, arising from a triangular mucro about | line long (which is always present, 
though the hair-like extension may not be visible). Frond composed of 2 reflexed 
branches, commonly about 9 lines long and 1 line wide to the tips of the denticles, 
the denticles at this size being 7 or 8 in 3 lines, but occasionally 1 in. 9 lines long, 
and then 3 lines wide, and with only 5 to 6 denticles in 8 lines; the branches are 
continuously rounded semi-elliptically at their junction, and nearly as wide there as 
at any other part, slightly wider a little beyond the junction, and thence slightly 
narrowing to the extremities, the outer edge forming tangents to the basal curve ; 
inner edges almost straight, and diverging at an angle varying (without relation to 
size) from 50° to sub-parallel, and 3 lines apart, owing to the small abrupt rounding 
of the inner edge at the junction with the short angular mucronate base of the 
radicle. The denticles form a continuously uniform row along the outside of the 
branches and connecting curve; they are small, triangular, slender, gradually pointed, 
and slightly arched downwards; their lengths slightly more or less than the space 
between their points; the contiguous upper and lower edges of the denticles forming 
an oblique elliptical notch, not angulated; the thickened lines from the denticles 
forming the lower boundary of each cell are arched near the outer end, and nearly 
straight and very oblique as they extend downwards and towards the inner edge 
of the branch opposite the third lower denticle, but becoming much more oblique 
(opposite 5th denticle) near the ends of the branches, and much less oblique towards 
the rounded junction of the arms when they are almost direct and nearly at right 
angles to the margin. The denticles indent the branch rather less than half a line 
when they are nearly 3 lines wide, and are very slightly less when the branches are 
only 1 line wide, so there is no relation between these proportions. The ends of 
the branches when perfect are obliquely rounded parrallel to the cell lines. Very 
young specimens resemble an expanded fan between 2 and 8 lines in diameter, with 
about 14 radiating cell lines, divaricating through nearly three-fourths of a circle 
and terminating in denticles of the size and shape of those of adults; the central 
mucro resembles the handle of the fan. 
REFERENCE.—(Salter), Quarterly Journl. Geol. Soc. Lond., vol. ix., p. 87. 
The figures given as above by Mr. Salter, more than 3 an inch 
long, show the branches little less than a line wide excluding the 
points of the cells, and scarcely exceeding a line wide including 
them ; the central spine is about 3? of an inch long, and the 
denticles are represented as almost 7 in 3 lines, and the lateral 
branches are figured and described as sub-parallel or only diverging 
at about 20°. Such specimens occur occasionally in Victoria, but 
they are poorly developed and unusual ; the more common speci- 
mens being intermediate between the small state and the large 
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