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XVIII.—On the Structure and Affinities of Tristichopterus alatus, Egerton. 
By Ramsay H. Traquair, M.D., F.G.S., Keeper of the Natural History 
Collections in the Museum of Science and Art, Edinburgh. (Plate 
XXXII.) 
(Read April 5, 1875.) 
Concerning the affinities and systematic position of this very remarkable 
Devonian fish, there has hitherto prevailed very great uncertainty. The two 
original specimens, discovered by Mr C. W. Peacu, in the Old Red Sandstone 
of John O’Groat’s, Caithness, and described by Sir Puitie Ecrrton,* left us in 
complete ignorance as to the .osteology of the head and the dentition, while the 
evidence they afforded as to the structure of the pectoral fins was by no means 
so clear as might have been wished for. To quote from Sir Pxixip’s descrip- 
tion:—‘‘The bones of the head, with the exception of a small fragment of the 
operculum, are wanting, but the impressions left upon the matrix show that 
they were sculptured in rather a bold pattern, not unlike the ornament on 
some of the cranial bones of some of the Holoptychii, and consequently differing 
in this respect from the corresponding parts in Dipierus. The pectoral fins are 
very indistinctly seen. They appear to have had a short obtuse lobe forming 
the base, and extending therefrom a set of numerous fin-rays more elongated 
than those forming the pectoral fin in Dzpterus.” To Dipterus, however, in Sir 
Puitie EceRtToN’s opinion, its affinities pointed, as far as could be gathered 
from the structure of the body as displayed in the specimens, his description 
concluding as follows:—‘ The absence of all evidence as to the dental apparatus 
of Tristichopterus is much to be regretted. On other points the affinities 
between this genus and Dipterus are so striking that they cannot be classified 
in separate families.t Accordingly he assigned to Tvristichopterus a place along 
with Dipterus in the family of “ Coelacanthi,” the term being used in its former 
extended sense, not as now restricted to the peculiar genera Colacanthus, 
Undina, Holophagus, and Macropoma. 
Professor Huxtey, at the conclusion of his Essay on the Classification of the 
Devonian Fishes,{ published in the same Decade of the Geological Survey, 
makes the following statement regarding the genus in question:—‘ In the 
absence of a full knowledge of the head, of the paired fins, and of the dentition, 
* Dec. Geol. Survey, x. 1861, pp. 51-55, pl. v. t Loe cit. p. 55. 
$ Dec. Geol. Survey, x. 1861, p. 40. 
VOL. XXVII. PART III. DH 
