Dr. R. H. Traquair—Old Red Sandstone Fishes. 515 
which genus it still further resembles in having the laniaries com- 
pressed and two-edged towards the apex; these laniaries are how- 
ever proportionally much smaller in size, and the internal denticles 
which support them different in shape from those of Rhizodus, being 
broad and flat, instead of narrow and compressed. This species may 
probably turn out to be generically referable to Cricodus, Ag., which, 
judging from Agassiz’s figures of C. incurvus and of Polyplocodus 
given by Pander, is certainly a Rhizodont. It will be remembered 
that ‘ Polyplocodus” was the name by which Pander sought to dis- 
place “ Cricodus,” on the ground that the latter was descriptively 
inaccurate. 
RHOMBODIPTERIDE. 
It is remarkable that although Zittel, in his “ Handbuch,” includes 
the Rhizodonts in one heterogeneous family with the Holoptychi, he 
nevertheless keeps the Rhombodipterines apart, whose close affinity 
with the Rhizodonts I have indicated in my memoir on the Cranial 
Osteology of Rhizodopsis already quoted. In fact much is to be said 
in favour of Prof. Miall’s plan of uniting the Rhizodonts and 
Rhombodipterines in one group, and in this connection I may 
mention the recent discovery by Mr. J. Ward, F.G.S., of a specimen 
apparently of Rhizodopsis on the scales of which there is undoubted 
evidence of ganoine, while I think I have myself observed the same 
phenomenon in the case of the fin-rays of a specimen of Gyroptychius 
microlepidotus from Tynet. But I shall for the present adhere to 
the arrangement given in my essay on Tristichopterus, thereby 
dividing the Rhombodipteride into two subfamilies—Glyptolemini, 
in which the scales are sculptured and destitute of ganoine, and 
Saurodipterini, in which the scales are covered with a layer of 
ganoine and the elements of the cranial roof and of the mandible 
have a tendency to fusion with each other. 
SAURODIPTERINI. 
Osteolepis, Val. and Pentland.—The genus Osteolepis is mentioned 
by Sedgwick and Murchison as having been named by Valenciennes 
and Pentland with two species, macrolepidotus and microlepidotus, 
but, unfortunately, neither figures nor adequate descriptions are 
given, though Pander identifies as “‘ Osteolepis” the figure given in 
the same paper as that of a young individual of “ Dipterus” 
macrolepidotus. Agassiz afterwards adopted the name Osteolepis in 
place of his own “ Pleiopterus,” and described the species macro- 
lepidotus and microlepidotus from the specimens from Orkney in the 
collection of Prof. Traill. Here I must agree with Pander that 
Agassiz’s ‘‘ microlepidotus” is identical with his macrolepidotus, and 
I feel indeed doubtful if even the latter is the same fish with that 
originally so named by Valenciennes and Pentland, as I have never 
convinced myself of its occurrence in the Caithness beds at all. 
And I must also agree with Pander in considering that the Osteolepides 
from the Moray Frith nodules, namely, “arenatus,” Ag., and “major,” 
Ag., are both synomymous with O. macrolepidotus from Orkney, and 
only differ in their mode of preservation. O. brevis, McCoy, of 
