MANSFIELD DISTRICT, VICTORIA. 
the pectoral fin-spines, hut the second specimen cannot be 
explained in this manner. It is thus probable that there was a 
small anterior dorsal fin, with a spine, situated opposite to the 
insertion of the pair of pelvic fins. A posterior dorsal fin, opposed 
to the sjiace between the pelvic and anal fins, is more satisfac- 
torily preserved (PI. V, fig. 1). Its slender anterior spine is 
nearly straight, and shown in a broken longitudinal section, which 
exposes the large internal cavity and appears to suggest that it 
bore an external coarse tubercular ornament of some kind. The 
fin itself is covered with dermal tubercles like those of the trunk. 
The length of its base-line seems to have slightly exceeded the 
height of its anterior spine, which can scarcely have equalled less 
than two-thirds the depth of the trunk at its insertion. The 
anal fin-spine, inserted opposite the hinder end of the posterior 
dorsal fin, is not much more than half as long as the dorsal fin- 
spine just described ; but it is similar in character, with a very 
large central cavity. Its outer face is not seen in PI. V, fig. 1, 
but an impression of it on the counterpart of the specimen repre- 
sented in PL I, fig. 7 (see fig. Id) exhibits an external ornament 
of a few large, tuberculated ridges, which are disposed longitudi- 
nally parallel with the hinder border and successively terminating 
at the front edge. One of the two specimens showing the anal 
fin-spine must be distorted, for in PI. I., fig. 7, this spine (c) is 
observed quite near the apex of the pelvic fin-spines, while in PI. 
V, fig. 1, it is further back (probably its natural position). The 
very stout caudal fin (PI. V, fig. 1) is of the usual Acanthodian 
type, with no clear line of demarcation in the fossil between the 
upper caudal lobe and the dermal expansion beneath it. 
Dermal Tubercles . — Both head and trunk are enveloped 
in a close and uniform covering of calcified dermal tubercles, 
which are not enlarged or modified even along the course of the 
lateral line. They are rhombic, usually almost equilateral in 
sliajie, and closely pressed together. Their inner face, seen on 
parts of the type-specimen, is flattened or even slightly concave, 
and it is pierced in the middle of the opening of a small, persis- 
tent pulp-cavity (PI. I, fig. 1 a). Their outer face is raised in 
the middle into a rounded boss, which sometimes exhibits a 
[ll] 
2a 
