158 
ACTIXOPTERYGII. 
caudal fin. Pelvic fins arising much nearer to the anal than to the 
pectorals ; the dorsal fin, with about 24 rays, arising considerably 
in advance of the middle point of the hack and extending nearly to 
the base of the caudal fin ; the anal fin, with 17 rays, opposed to 
the hinder two-thirds of the dorsal, and the length of its foremost 
ray equalling nearly half of the maximum depth of the trunk. The 
thickened abdominal squamation terminating abruptly at a line 
joining the origin of the dorsal and anal fins. 
Form. Sf Log. Upper Hawkesbury-Wianamatta Series : Talbralgar, 
New South Wales. 
Not represented in the Collection. 
Genus TETRAGONOLEPIS, Bronn. 
[Neues c ahrb. 1830, p. 30.] 
Syn. Tleurolepis , F. A. Quenstedt, Handb. Petrefakt. 1852, p. 214. 
Homceolepis , A. Wagner, Gelehrte Anzeig. k. bay. Akad. Wiss. 
1860, p. 92. 
Trunk much laterally compressed, cycloidal or very deeply 
fusiform, and the abdominal region relatively large, protuberant 
ventrally. Head comparatively small, with well-developed oper¬ 
cular bones arranged in an arched series ; preoperculum narrow; 
the external bones in part ornamented with superficial tubercula- 
tions of ganoine. Marginal teeth styliform, in close regular series. 
Notochord persistent, apparently with pleurocentra and hypocentra; 
ribs short but ossified ; neural spines fused with their supporting 
arches throughout, and both neurals and hsemals in caudal region 
with laminar expansion on anterior border. Fins consisting of 
distally bifurcating rays; paired fins small, the pectorals situated 
at about the middle of the flank, the pelvic fins remote; dorsal 
fin much elongated, arising about the middle of the back, and 
anal fin shorter, opposed to the hinder half of the dorsal; caudal 
fin only slightly, if at all, forked. Scales quadrangular, very deep 
on the flank, smooth, rugose, or tuberculated, and the anterior 
border strengthened by a robust inner rib, which forms the peg- 
and-socket articulation; caudal scales much thinner than those of 
the abdominal region ; ventral ridge-scales conspicuous, serrated. 
Tetragonolepis semicincta, Bronn. 
[Plate III. fig. 1.] 
1830. Tetragonolepis semicinctus, H. G. Bronn, Neues Jahrb. p. 30, 
pi. i. fig. 2. 
1832. Tetragonolepis semicinctus , L. Agassiz, Neues Jahrb. p. 147. 
