DR. A. GUNTHER’S DESCRIPTION OE CERATODUS. 
r r r 
000 
Subfamily Protopterina. Conus arteriosus with two longitudinal 
valves. Ovaries closed sacs. One continuous vertical fin: 
Lepidosiren , Protopterus. 
Fain. h. Ctenododipteridas. Caudal fin heterocercal ; gular plates. 
Scales cycloid. Two pairs of molars and one pair of 
vomerine teeth : Dipterus. 
1 (Fam. c. Phaneropleuridce. Caudal fin diphycercal ; gular plates. 
Scales cycloid. Jaws with a series of minute conical 
teeth on the margin : Phaneropleuron.) 
On the Affinities of Ceratodus to certain Fossil Fishes. 
Those who have followed the researches made of late years into the affinities of Ga- 
noid fishes, must have remarked that in the conclusion of the preceding chapter I have 
touched upon a subject which had been approached by Professor IIuxley from a palaeon- 
tological point of view*. One result of his examination of the Devonian fishes was 
the establishing a separate suborder of Ganoids, Crossopteryyidce , which comprises the 
Ganoids provided with fringed or lobate fins and generally with gular plates, branchio- 
stegals being absent. This suborder was divided by him into five families of extinct 
fishes, chiefly from the Devonian epoch, viz. Saurodipterini, Glyptodipterini , Ctenodo- 
dipterini , Phaneropleurini, and Ccelacanthini ; Polypterus was associated with them as 
* “ Preliminary Essay upon the Systematic Arrangement of the Fishes of the Devonian Epoch,” by T. II. 
Huxley, F.R.S., in Mem. Geolog. Survey, Dec. 10, 1861. At that time, when Lepidosiren was still the only repre- 
sentative of Muller's subclass Dipnoi, Professor Huxley pointed at its affinity to certain Ganoids: — “Without 
wishing to lay too much stress upon the fact, I may draw attention to the many and singular relations which 
obtain between that wonderful and apparently isolated fish, Lepiclosiren, sole member of its order, and the cycloid 
Glyptodipterine, Ctenododipterine, Phaneropleurine, and Coelacanth Crossopterygidm. Lepidosiren is, in fact, 
the only living fish whose pectoral and ventral members have a structure analogous to that of the acutely lobate, 
paired fins of Holoptychius, of Dipterus, or of Phaneropleuron, though the fin-rays and surface-scales are still 
less developed in the modern than in the ancient fish. The endoskeleton of Lepidosiren, again, is as nearly as 
possible in the same condition as that of Phaneropleuron, and is more nearly similar to the skeleton of the 
Ccelacanths than that of any other recent fish [ qucere Acipenser ? A. G.] ; while, perhaps, it is not stretching the 
search for analogies too far to discover in the stiff-walled lungs of Lepidosiren a structure more nearly repre- 
senting the ossified air-bladder of the Coelacanths than any With which we are at present acquainted, among 
recent or fossil fishes. Furthermore, Lepidosiren is the only fish whose teeth are comparable in form and 
arrangement to those of Dipterus. Though Lepidosiren may not be included among the C rossopterygidce, nor 
even in the order of Ganoidei, the relations just pointed out are not the less distinct; and perhaps they gain in 
interest when we reflect that while Polypterus, the modern representative of the rhombiferous Crossopterygidoe, 
is that fish which has the most completely lung-like of all air-bladders, Lepidosiren, which has just been shown 
to be, if not the modern representative of the cycliferous Orossopterygidce, j _ et their ‘ next of kin,' is the only 
fish which is provided with true lungs. These are unquestionable facts. I leave their bearing upon the great 
problems of zoological theory to be developed by every one for himself.” 
