OO A ATT 
(ae) 
XX.—Supplement to the Lower Devonian Fishes of Gemiinden. By R. H. Traquair, 
M.D., LL.D., F.R.S., Keeper of the Natural History Collections in the Royal 
Scottish Museum, Edinburgh. (With Three Plates.) 
(Read December 19, 1904. Given in for publication April 14, 1905. Issued separately May 13, 1905.) 
Since the publication, about a year ago, in the Transactions of this Society, of my 
paper on the Lower Devonian Fishes of Gemiinden,* a review of it has appeared in the 
pages of Science by Professor Basnrorp Dean, of New York. In this review Professor 
DEAN endeavoured to throw doubts on the correctness of my orientation of the elements 
of the dermal skeleton of Drepanaspis Gemiindenensis, in the following words : t— 
“Thus, his grounds seem inadequate for distinguishing dorsal and ventral sides. 
In no specimen figured is the relation of the dorsal lobe of the tail shown convincingly 
to be continuous with the so-called dorsal aspect ; moreover, the eyes occur on the side 
which Traquair regards as ventral. Unless additional evidence is forthcoming, it would 
accordingly seem to me more probable that the ‘labial’ { of TRaquarr was the ‘rostral’ 
plate, a structure which appears constant in Heterostracans. ‘This interpretation would 
permit the eyes to be seen at the sides of the dorsal armoring, as indeed they occur in 
Pteraspis, and would enable us at the same time to locate the greater number of the 
larger plates on the dorsal side. This conclusion is the more satisfactory on com- 
parative grounds, since there is not an instance in the chordate phylum in which the 
eyes and the most complete part of the armoring appear on the (morphological) ventral 
side. And I doubt whether, on the present evidence, we can assume, with Professor 
Patren, that Drepanaspis might have evaded the law of vertebrate orientation by 
swimming on its back. Dr TRaquarr has attempted to solve this dorso-ventral difficulty 
by suggesting that either the orbits are ‘sensory’ pits, 7.e. not orbits, or that, ‘since the 
specimens are all crushed absolutely flat, it is by no means certain that in the original 
uncompressed condition the openings did not look out to the side.’” 
The tail of Drepanaspis being heterocercal, the dorsal aspect of the caudal fin, in 
accordance with the universal condition of such tails among fishes, will be that along 
which the prolongation of the body-axis proceeds, as shown by its greater extent, by 
the squamation, and more especially by the larger size and (usually) greater number of 
the ridge scales or “fulcra.” In the above-quoted criticism Professor BasHrorp DEan 
gave it as his opinion that I had failed to prove that this dorsal aspect of the tail was 
coincident with that aspect of the carapace which I described as dorsal, and which he, 
* “The Lower Devonian Fishes of Gemiinden,” Trans, Roy. Soc. Edin., vol. x1., Part iv., October 1903. 
t Science, N.S., vol. xix., No. 471, January 8, 1904. 
{ The plate here meant is in my memoir termed mental, and not “labial.” 
TRANS. ROY. SOC. EDIN., VOL. XLI. PART II. (NO. 20). 70 
