Gobioidei, Discocephali, and Teniosomi 679 
The family of Oxudercide contains one species, Oxuderces 
dentatus, a small goby-like fish from China. It is an elongate 
fish, without ventral fins, and with very short dorsal and anal. 
Suborder Discocephali, the Shark-suckers: Echeneidide.—Next 
to the gobies, for want of a better place, we may mention the 
singular group of Discocephali (dioxos, disk; xepydn, head). 
In this group the first dorsal fin is transformed into a peculiar 
laminated sucking-disk, which covers the whole top of the head 
and the nape. In other respects the structure does not diverge 
very widely from the percoid type, there being a remarkable re- 
semblance in external characters to the Scombroid genus Rachy- 
centron. But the skeleton shows no special affinity to Rachy- 
centron or to any perciform fish. The basis of the cranium is 
Fic. 592.—Sucking-fish, or Pegador, Leptecheneis naucrates (Linnzus). Virginia. 
simple, and in the depression of the head with associated modi- 
fications the Discocephali approach the gobies and blennies 
rather than the mackerel-like forms. 
The Discocephali comprise the single family of shark-suckers 
or remoras, the Echeneidide. All the species of this group 
are pelagic fishes, widely diffused in the warm seas. All cling 
by their cephalic disks to sharks, barracudas, and other free- 
swimming fishes, and are carried about the seas by these. They 
do not harm the shark except by slightly impeding its move- 
ment. They are carnivorous fishes, feeding on sardines, young 
herring, and the like. When a shark, taken on the hook, is 
drawn out of the water the sucking-fish leaves it instantly, 
and is capable of much speed in swimming on its own account. 
These fishes are all dusky in color, the belly as dark as the back, 
so as to form little contrast to the color of the shark. 
The commonest species, Leptecheneis naucrates, called pega- 
pega or pegador in Cuba, reaches a length of about two feet 
and is almost cosmopolitan in its range, being found exclusively 
on the larger sharks, notably on Carcharias lami. It has 
