Salmoperce and Other Transitional Groups 243 
short dorsal has two or three spines, there are two or three 
spines in the anal, and the abdominal ventrals are opposite 
the dorsal. Allied to Eris- 
matopterus is Amphiplaga of 
the same deposits. 
We cannot, however, feel 
sure that these extinct frag- 
ments, however well preserved, 
belonged to fishes having an 
adipose fin. Among spiny- 
rayed fishes the Percopside 
alone retain this character, and 
the real affinities of Erisma- 
toplterus may be with A phredo- 
deride and other  percoid 
forms. 
The relations of the extinct 
family of Astneopide are also 
still uncertain. This group 
comprises fresh-water fishes 
said to be allied to the A phre- 
doderide, but with the pelvic 
bones not forked. Asineops 
pauciradiata, squamifrons and 
viridensts are described from 
the Green River shales. With 
Erismatopterus all these fishes 
may belong to the suborder 
of Salmoperce, but, as above 
stated, the possession of the adipose fin, the most characteristic 
trait of the Salmoperce, cannot be verified in the fossil remains. 
Suborder Selenichthyes, the Opahs: Lamprididea.—We may bring 
together as constituting another suborder certain forms of uncer- 
tain relationship, but which seem to be transitional between 
deep-bodied extinct Ganoids and the forms allied to Platax, 
Zeus, and Antigonia. The name of Selenichthyes (ondnvn, moon; 
iydus, fish) is suggested by Boulenger for the group of opahs, 
or moonfishes. These are characterized by the highly com- 
pressed body, the great development of a large hypocora- 
