MANSFIELD DISTRICT, VICTORIA. 
Gyracanthus' and Oracanthus’. The narrow-ovoid basal opening 
of the large internal cavity of this spine is closed in two specimens 
by a separate basal plate, which seems to be in its natural 
position. ‘This plate is well shown in the drawing of one side of 
the type-specimen (Pl. I, fig. 14), and again in PI. II, fig. le. 
It is quite as thin as the conical wall of the spine itself, and is 
clearly a separate element, calcified from its centre, from which 
structural lines radiate outwards. It exhibits traces of a tuber- 
cular ornament or of overlying shagreen-granules in both 
specimens. Its true nature is thus very difficult to understand, 
and it may even have been somewhat displaced in the fossils. 
Pelvic Fin-spine.—The spines of the pelvic fins are very 
little more than half as large as those of the pectoral pair, while 
they are much more rounded in transverse section and straighter 
than the latter. The pelvic fins themselves are advanced so far 
forwards that the points of their spines scarcely extend backwards 
beyond those of the pectoral spines. Only one displaced pelvic 
spine is partly seen in an accidental fracture of the type- 
specimen, but the relative position of the pair is indicated 
mei L, fig. 7 {e;%e'), PL. TL fig? 2) (¢),. Pl. TEL ieee, 
and Pl. V, fig. 1. In the first two figured examples just 
mentioned, each spine is represented solely by a natural mould of 
its internal cavity with scarcely any impression of the ornamented 
exterior face. In the original of Pl. ITI, fig. 1, however, where 
the spines are somewhat crushed together, fragments of their 
actual tissue are preserved, and impressions of their basal ends 
show the characteristic ornament forming parallel V-shaped 
ridges on the rounded lower face. In the original of PI. V, fig. 
1, there is also the basal end of the spine itself (a). These 
specimens, and the impression of one side of a detached example 
(text-fig. 2), show that the pelvic fin-spine was ornamented like 
the pectoral fin-spine, with continuous, tuberculated ridges, which 
are separated by comparatively wide, smooth grooves. The 
ridges tend to a more and more longitudinal direction as they are 
1 A. S. Woodward, “Catal. Foss. Fishes, B.M.,” pt. ii. (1891), p. 143. 
2 J. W. Davis, loc. cit. 
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