566 
ACTINOPTEKYGII. 
About four dorsal spines, the foremost 
only large; posterior dorsal and 
anal fins low but extended ; pair 
of pelvic fin-spines Acanthopleurus (p. 566). 
About three dorsal spines, the foremost 
only large ; posterior dorsal and 
anal fins low but extended; no 
pelvic fins Acanthoderma (p. 568). 
II. With polygonal dermal plates. 
No spinous dorsal or pelvic fins ; der- 
mal plates forming rigid armour . Ostracion (p. 669). 
Genus SPINACANTHUS, Agassiz. 
[Poiss. Foss. vol. v. pt. i. 1844, p. 107.] 
Syn. Protobalistum, A. de Zigno (e.r Massalongo, MS.), Mem. Soc. Ital. 
Sei. [3] vol. vi. no. 4, 1885, p. 3. 
Teeth very stout, apparently in single series. Pectoral fins 
delicate ; [pelvic fins unknown ; ] six or seven very largo dorsal 
spines in spaced series extending from above the eye along more 
than half of the dorsal border, gradually decreasing in si ze 
backwards; posterior dorsal and anal fins relatively small and 
short-based ; caudal fin rounded. Dermal tubercles minute. 
This extinct genus is known only by two imperfect specimens 
from the l pper Eocene of Monte liolca, near Yeroua; the first 
being in the Paris Museum of Natural History, described and 
figured by Agassiz (Poiss. Eoss. vol. v. pt. i. 1839-44, p. 107, 
pi. xxxix. fig. 1) under the name of Spinaeanthus blennioides ; the 
second in the Yerona Museum, described and figured by A. de 
Zigno (Mem. Soc. Ital. Sci. [3] vol. vi. no. 4, 1885, p. 4, figs. 1, 2) 
under the name of Protobalistum imperiale. The first specimen 
differs from the second in exhibiting serrations on the anterior 
dorsal spine. It was originally ascribed in error to Blennius 
ocellaris by G. S. Yolta (Ittiolit. Yoronese, 1796, p. lxiv. pi. 
fig. 2), and subsequently named Blennius cuneiformis by H. D. de 
Blainville (Nouv. Diet. d’Hist. Nat. vol. xxvii. 1818, p. 359). 
The second specimen was originally recorded under the name of 
Ostracion imperials by A. B. Massalongo (Neues Jahrb. 185 1 , 
p. 775). 
Genus ACANTHOPLEURUS, Agassiz. 
[Poiss. Foss. vol. ii. pt. ii. 1844, p. 253.] 
A supposed extinct genus, not yet clearly distinguished from the 
existing Triacanthus. [Teeth unknown.] [Pectoral fins unknown ; ] 
