Dll. A. GUNTHER’S DESCRIPTION OE CERATODUS. 
557 
nothing hut a genus most nearly allied to Ceratodus, as shown by the arrangement of 
its three pairs of teeth, form of the snout, position of nostrils, acutely lobate fins, 
&c. ; the presence of the gular plates alone might have offered ground for hesitation. 
Yet, when we examine the tail, we find that the one genus is truly diphycercal, the 
other eminently heterocercal, so that they cannot remain even in the same family. I 
do not attach much importance to the separation of the vertical fins, or to the division 
of the dorsal into two ; such modifications are common in the Gadoid fishes, where they 
are considered to be scarcely of generic value. Of much greater importance is the junc- 
tion of the dermal fin-rays with the supporting spines, and the position of the dorsal 
fin or fins. In the former point Dipt eras differs from Ceratodus; in the latter both 
genera agree. 
Weighing the points of affinity and difference against each other, Ave must come to 
the conclusion that Dipterus has a better right to be associated Avith the living Dipnoi , 
than with Polypterus. 
Wherever Dipterus and Ceratodus are placed, thither Cheirodus (M‘Coy, Pander) or 
Conchodus (M‘Coy) must folloAv. But it is probable that this genus is more nearly allied 
to Ceratodus. 
At first I thought that Holodus (Pander) was another Dipnoous genus ; but I changed 
this opinion after having compared it Avith Palcedapkus of Van Beneden and De Ko- 
ninck (Bull. Ac. Roy. Belg. 2nd ser. xvii. p. 151, pis. 3 & 4). These two genera are 
evidently closely allied ; and the position of their nostrils (as far as Ave can judge from 
the fragmentary remains) appears to have been different from that of the Dipnoi ; these 
openings Avere more lateral, and outside of the mouth. It seems also that there would 
not have been room for a pair of vomerine teeth, at least not in Palcedapkus. 
There are tAvo other genera of fossil fishes of the Devonian epoch Avhich have been 
referred to the Crossopterygians, and which appear to approach the Dipnoi more closely 
than the other fringe-finned fishes, viz. PJianeropleuron and Tristichopterus. With 
regard to the former genus I refer to Professor Huxley’s description and figures in 
Anderson’s ‘ Dura Den,’ p. 67 et seqq. , and Mem. Geol. Surv. Dec. 10, p. 24 et seqq. 
The structure of the skeleton of the trunk and tail and of the fins is extremely similar 
to that of Ceratodus. In those specimens in which I found the foremost part of the 
snout tolerably well preserved, no interruption in the surface of the osseous ^substance 
could be discovered ; and therefore it is not improbable that the nasal openings were inside 
the mouth as in Dipnoi. On the other hand, minute conical teeth in rather small number 
Avere visible in the margins of the upper as Avell as loAver jaAV, thus indicating by 
their presence a development of maxillary elements which are entirely missing in the 
Dipnoi. 
The genus Tristichopterus Avas established and described by Sir PuiLir Egerton in 
Mem. Geol. Surv. Dec. 10, p. 51 et seqq., where already the affinities of this highly inter- 
esting fish to Dipterus Avere fully considered by its author. The fins Avere composed 
of innumerable fine fin-rays closely placed together, and overlapping with their proximal 
