470 DR R. H. TRAQUAIR ON 
from other reasons, thought much more likely to be ventral. In other words, I had 
turned the fish upside down. 
It was, however, satisfactory to read in the same periodical, a few months later, the 
following counter-criticism by another eminent American paleeichthyologist, Dr C. R. 
Hastman, of Cambridge, Massachusetts :— 
‘Whatever may be thought of Traquarr’s figures, though his Plate II. seems to us 
conclusive enough, there can be no question about the originals, and those who have 
examined them attentively are compelled to admit the correctness of the Scottish 
author’s interpretations. The dorsal ridge-scales are larger than the ventral and form 
a more extended series, beginning further forward and continuing further back than the 
ventral fulera, Several specimens in the Edinburgh Museum have been pointed out to 
the present writer by Dr Traquarr in which this row of prominent ridge-scales can be 
traced continuously from a point shortly behind the median dorsal plate to the tip of 
the dorsal lobe of the tail. The extent to which the caudal lobes are covered with 
fulcra is well shown in Plate IV. and Plate [. fig. 1 of the memoir in question, and 
their connection with upper and lower systems of body-plates appears tolerably 
distinct.” * 
For my part, I certainly hold that the relations of the heterocercal tail to the 
two surfaces respectively of the carapave were quite satisfactorily proved in the plates 
plus text of my former paper. The great median plate of the surface on which 
the mouth and supposed orbits are placed, I described as being different from the one 
on the other side (see Plates I., II., and IV.) by being bilobate in front, and having 
behind a peculiar raised longitudinal fold continuing the direction of the posterior 
notch a little way forwards. It is true that I did not, among my plates, reproduce a 
photograph of an entire specimen of this plate, the one shown in Pl. III. being 
deficient posteriorly, but in the text-figure 3, p. 729, I “ restored its contour from other 
specimens” (p. 728). And in the specimen, of which a good photograph is given, in 
Pl. V. fig. 1, the line of smaller fulera, situated on the presumably ventral margin of 
the tail, is exhibited with absolute clearness running up to the posterior (cloacal) notch 
of that plate, which, as shown by its prominent median fold, is as undoubtedly the plate 
described by me as ventral. 
But as Professor DEan’s remarks have been widely circulated in so well-known a 
periodical as Sczence, I shall in this “Supplement” go over the subject of the orienta- 
tion of the exoskeleton of Drepanaspis once more, this time illustrating by specimens 
not figured in my previous memoir, though one of them (Pl. I.) was before me 
when it was written. 
The depressed and flattened carapace of Drepanaspis shows in front a wide mouth- 
slit, which, though nearly terminal, is not quite so, and consequently is seen only on 
one aspect of the creature, which may meanwhile be called the oral one. It 
* Science, N.S., vol. xix., No. 487, April 29, 1904, p. 704. 
