514 Dr. R. H. Traquair—Old Red Sandstone Fishes. 
Family Rurzopontipz. 
The Rhizodonts are not nearly so prominent a group in the Old 
Red Sandstone as in the Carboniferous rocks, nevertheless their 
presence both in the Lower and Upper divisions of the first-named 
formation is attested by several well-marked genera, such as 
Tristichopterus, Egert., from the Lower Old Red of Caithness, and 
Eusthenopteron, Whiteaves, from the Upper Devonian of Canada. 
There are also others to which I shall now refer. 
Gyroptychius, McCoy.—For many years I was much puzzled by 
this genus, which— originally referred to the ‘‘Coelacanthi” by McCoy 
—was classed as a ‘“‘Dendrodont” by Pander, and as a ‘Sauro- 
dipterine” by Egerton. Huxley also placed it in the rhombiferous 
division of his Glyptodipterini; but if Pander’s figures are taken 
from authentic examples of Gyroptychius angustus, McCoy, we have 
to deal with a typically Rhizodont genus. Accordingly in my 
account of Tristichopterus alatus (Trans. Roy. Soc. Edin. vol. xxvii. 
1875) I placed it in the group of Cyclodipteridee (Cyclodipterini 
Liitk. excl. Holoptychiidz), the family designation of which I 
afterwards altered to “ Rhizodontide ” (Cranial Osteology of Rhizo- 
dopsis, ib. vol. xxx. 1881). Not having at that time (1875) seen 
the original specimens, I appended a query, owing to the apparently 
rhombiferous squamation of G. diplopteroides, McCoy. Since that 
time a careful examination of the types in the Woodwardian Museum, 
Cambridge, has afforded the following explanation of the puzzle. 
Gyroptychius diplopteroides is nothing but a specimen of Diplopterus 
Agassizit, Traill (D. borealis, Ag.), with the ganoid surface of the 
scales wanting, as is so often the case in Orkney specimens, while 
G. angustus is valid generically, is a Rhizodont, and no doubt the 
same as the fish whose details have been figured and described by 
Pander. But more than this, on examining a series of specimens of 
Glyptolepis microlepidotus, Ag., including the types, I was interested 
to find that this fish had obtusely lobate pectorals, and labyrinthically 
folded tooth-bases, and is therefore not a Glyptolepis nor even a 
Holoptychian, but a Rhizodont. And on comparing those Moray 
Frith specimens with those from Orkney referable to McCoy’s 
Gyroptychius angustus, so close is the resemblance between the 
rhombic diphycercal shape of the tail, the position of the fins, the 
shape and markings of the scales, and other details, that ] am 
forced to the conclusion that Glyptolepis microlepidotus, Ag., and 
Gyroptychius angustus, McCoy, are one and the same thing. The 
genus Gyroptychius therefore stands, but G. diplopteroides must be 
cancelled, and for the type species “ microlepidotus,’ Ag., must be 
substituted for ‘ angustus,’” McCoy. I may remark that Gyroptychius 
is one of those genera which, like Rhizodopsis of the Carboniferous, 
closely bind together the families of Rhizodontide and Rhombo- 
dipteridee. 
Another Rhizodont genus of the Old Red Sandstone (Upper) is 
represented by the Bothriolepis favosus of Agassiz, a mandible of 
which, from Clashbennie, in the Hdinburgh Museum: clearly shows 
that the teeth were labyrinthically folded at the base as in Rhizodus, 
