Dajaus Diemensis, _Richards._ in Proceed. of Zool. Soc. 1840, p. 25.
This genus, which was established by Cuvier and Valenciennes, differs
from _Mugil_ principally in having vomerine and palatine teeth: the
snout also is rather more produced, and the mouth less chevron-formed.
There is but one species described in the “Histoire des Poisssons,”
which is found in fresh water in the Caribbee Islands. Dr. Richardson
has briefly noticed a second from Van Diemen’s Land, in his recent
description of a collection of fishes from that country, in the
“Proceedings of the Zoological Society.” Mr. Darwin’s collection
contains a specimen of this genus from King George’s Sound, which,
having reason to think it might be the same as that described by Dr.
Richardson, I sent to this latter gentleman, requesting him to compare
them. This he obligingly did, and informed me in his answer that he
could detect no differences between them, beyond what might be the
result of the different manner in which they were preserved, his own
specimens being in spirits, and Mr. Darwin’s dried.
I forbear giving a detailed description of this species, as one by Dr.
Richardson will appear shortly in the Transactions of the Zoological
Society; and Mr. Darwin’s specimen is in such a bad state of
preservation, as hardly to admit of an accurate description of it being
taken. I may just allude, however, to some of its more striking
peculiarities.
It appears to differ from the _D. monticola_ of Cuvier and
Valenciennes in having the teeth in the lower jaw, if they really
exist, so minute and thinly scattered as to be scarcely perceptible;
those in the upper jaw, however, are very distinct; so likewise are
the vomerine and palatine bands. There are also some very obvious
teeth on the tip, and at the sides of the tongue, though few in the
middle: this part is said to be without any asperities in the _D.
monticola_. The suborbital is more rounded off at the lower angle
anteriorly, and the denticulations thereon rather more numerous and
better developed. The scales on the body, those especially above the
lateral line, have a few minute teeth on their free edges,
communicating a roughness to the touch; a character not alluded to in
the description of the _D. monticola_, and which therefore may be
presumed absent. There are also three more rays in the anal, and one
in the second dorsal.
The depth of the body in this specimen, from its bad state of
preservation, cannot be ascertained; but the head is contained about
four and a half times in the entire length. The diameter of the
orbit is one-fourth the length of the head; and there is nearly one
diameter between it and the end of the snout. The jaws are nearly
equal, but when the mouth is closed, the upper one projects a
trifle; this last is also moderately protractile. The maxillary
retires beneath the suborbital. The fin-ray formula is as follows:—