444 
ELEMENTS OF GEOLOGY. 
Fig. 499. 
a. One of the fringed pectoral fins. h. One of the ventral fins. ,c. Anal fin. 
d. Dorsal fin, or row of finlets. 
analogy with Polypterus, They not only agree in the struc¬ 
ture of the fin, at first pointed out by Huxley, but also in the 
position of the pectoral, ventral, and anal fins, and in hav¬ 
ing an elongated body and rhomboidal scales. On the other 
Fig. 500. 
Restoration of Osteolepis. Pander. Old Red Sandstone, or Devonian. 
a. One of the fringed pectoral fins. b. One of the ventral fins. c. Anal fin. 
d, e. Dorsal fins. 
hand, the tail is more symmetrical in the recent fish, which 
has also an apparatus of dorsal finlets of a very abnormal 
character, both as to number and structure. As to the dor¬ 
sals of OsteolepiSj they are regular in structure and position, 
having nothing remarkable about them, except that there are 
two of them, which is comparatively unusual in living fish. 
Among the “fringe-finned” Ganoids we find some with 
rhomboidal scales, such as Osteolepis^ above figured; others 
with cycloidal scales, as Holoptychius^ before mentioned (see 
Fig. 498, p. 442). In the genera Dipterus and Diplopterus^ as 
Hugh Miller pointed out, and in several other of the fringe- 
finned genera, as in Gyroptychius and Glyptolepis^ the two 
dorsals are placed far backward, or directly over the ventral 
and anal fins. The Asterolepis was a ganoid fish of gigantic 
dimensions. A, Asmusi% Eichwald, a species characteristic 
of the Old Red Sandstone of Russia, as well as that of Scot¬ 
land, attained the length of between twenty and thirty feet. 
It was clothed with strong bony armor, embossed with star- 
like tubercles, but it had only a cartilaginous skeleton. The 
mouth was furnished with two rows of teeth, the outer ones 
small and fish-like, the inner larger and with a reptilian char¬ 
acter. The Asterolepis occurs also in the Devonian rocks of 
North America, 
