MANSFIELD DISTRICT, VICTORIA. 
occasionally in marine sediments. Their association with numer- 
ous remains of land-plants at Mansfield, however, is suggestive 
at least of estuarine conditions. They do not appear to exhibit 
any essential change as they are traced through the successive 
beds in the section so carefully worked and described by Mr. 
Sweet. 1 
II.— SYSTEMATIC DESCRIPTIONS. 
Subclass EL ASMO BRANCH II. 
Order Acanthodii. 
Family GYRACANTHIDiE. 
An imperfectly definable family of round-bodied and depressed 
Acanthodians, with the pectoral fins very large and the pelvic 
fins advanced far forwards. Dorsal and anal fins much reduced 
and sometimes apparently without spines. 
This family has hitherto been known only by detached paired 
fin-spines, other paired spines or plates, and small dermal 
tubercles, the majority belonging to one genus, Gyracanthus of 
Agassiz. The specimens of the new genus Gyracauthides now 
described, show for the first time the depressed, rounded form of 
the trunk and the relative position of the fins. 
Genus Gyracanthides, McCoy. 
[Ann. Rep. Sec. Mines, Victoria, 1889 (1890), p. 24.] 
Body short and broad. Teeth minute or absent ; no circutn- 
orbital plates. Both pectoral and pelvic fins with spines, the 
latter about half as large as the former. Pectoral fin-spines 
much compressed from above downwards, arched from side to 
side; their base of insertion extensive, with the internal cavity 
open for a considerable length posteriorly ; the longitudinal mesial 
line of their narrow anterior face defined by the superficial 
1 G. Sweet, “ On the Discovery of Fossil Fish in the Old Red Sandstone Rocks of the 
Mansfield District.”— Proc. Roy. Soc. Victoria, n.s., vol. ii., (1890), pp. 1-14, pis. 1-3. 
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