MANSFIELD DISTRICT, VICTORIA. 
body in a manner not unusual among Acantliodians. Remains 
of the anterior pair of these peculiar spines are observable on 
both sides of tlie type-specimen just in front of the base of tlie 
pectoral fin-spine (one shown at a in PL I, fig. 1). An internal 
cast of the corresponding spine in a second specimen is shown in 
PI. I, figs. 7 («), 7 a. An imprint of one face evidently of the 
same spine, somewhat displaced, is also seen in PI. Ill, fig. 1 
(c) ; and variously imperfect detached specimens are represented 
in PI. I, figs. 2-6. The structure is clearly a thin-walled, hollow, 
laterally-compressed cone, the length of its base-line equalling 
twice its height. Part of its calcified tissue is actually preserved 
in the type-specimen and in the original of PI. I, fig. 4, 
exhibiting a very porous texture (see especially PI. I, figs. 4 a, 
4 b) ; and impressions are marked by the appearance of fibres 
radiating from the apex, crossed by certain lines of growth which 
are concentric with the basal edge. There are traces of a coarse 
tubercular ornament at the apex of the best-preserved spine- in 
the type-specimen ; and this ornament is shown to be confined 
to one face of the spine in the detached example of which 
one lateral impression is represented in PI. I, fig. 2. The 
ornament consists of large, smooth tubercles arranged in ten 
to fourteen rows, which radiate from the apex and terminate 
at a short distance from the base of the spine, leaving a 
smooth area which was evidently the part originally inserted in 
the soft tissues. The tubercules increase in size towards the base 
of the spine, where they sometimes subdivide. As shown by 
various impressions (PI. I, figs. 2, 3, 5), this ornamented face bears 
much resemblance to a dental plate of the Dipnoan fish, Dipterus; 
but even when the rest of the spine is not seen, the fossil is 
distinguished from a Dipnoan dental plate by its sharply-defined 
smooth area beyond the termination of the radiating ridges. The 
base-line of this spine seems to have been more or less coincident 
with the long axis of the trunk, while its apex, as crushed in the 
best-preserved fossils, is turned outwards. 
Posterior Free Pectoral Spine . — The spine just described is 
not very large, the length of its base-line equalling only one-and- 
a-half times the maximum width of the pectoral fin-spine. The 
m 
