384 DR TRAQUAIR ON THE STRUCTURE AND AFFINITIES 
it would be hazardous to form any decided opinion as to the affinities of 
Tristichopterus; I strongly suspect, however, that it will turn out to be the 
type of a new family allied to the Ctenododipterini and Ceelacanthini.” How- 
ever, at page 24 of the same essay, he places it along with Dipterus in PANDER’s 
family of Ctenododipterini, though with a mark of interrogation. 
But when, in 1871, Dr GUnTHER* pointed out the close relationship between 
Dipterus and the recent Ceratodus and Lepidosiren, and the consequent 
desirability of transferring the first named genus to the group of Dipnoi, the 
question of course came up as to whether 77istichopterus should also accompany 
it thither. But to this no satisfactory answer could be given, so long as our 
knowledge on so many essential points of its structure was deficient. After 
referring to the manner in which the innumerable fine and closely-placed rays 
of the fins overlapped “with their proximal ends, the extremities of the inter- 
spinous bones, as in the Dipnoi,” and the peculiar form of the tail, which 
“represents a most curious intermediate condition between the diphycercal 
tail of the Szrenzdw and the heterocercal of Dipterus,” Dr GUNTHER con- 
cludes :—“ Unfortunately, the head and the base of the paired fins are destroyed 
in the only two specimens known; and it is chiefly the last-named character 
which prevents me from associating this genus with the Dipnoi.” 
No further description of the structure of Z7istichopterus having appeared 
since the publication of the Tenth Decade, I felt great satisfaction when Mr 
PEACH communicated to me a number of additional specimens, collected by 
him in the years 1864-65, and which throw a very great amount of the light 
desired on those points of its structure previously unknown to us.t These 
specimens exhibit in a clear and unmistakable manner the character of the 
dentition, the structure of the paired fins, and the leading features of the 
osteology of the head, and completely prove that Tristichopterus has no special 
affinity either with Dipterus or Celacanthus. Before, however, passing on to 
discuss the question of its real affinities and systematic position, I shall first 
proceed with the description of the new facts disclosed. 
General Proportions.—One of the specimens, the counterpart of which is in 
the British Museum, is quite entire, though the axis of the body is so curved 
as to render the dorsal margin considerably concave, the ventral corre- 
spondingly convex. The entire length of this specimen, carefully ascertained 
with a flexible measure, is 104 inches, of which the head occupies about 2th 
part; the greater depth of the body, just behind the subacutely lobate pectorals, 
being 2 inches. The general form of the fish is thus rather slender, and the 
fins are crowded towards the posterior aspect of the body,—the first dorsal 
commencing 6 inches, and the second 74 inches from the tip of the snout, 
* Description of Ceratodus, Phil. Trans. 1871. 
t These specimens are now in the Museum of Science and Art, Edinburgh. 

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