474 DR R. H. TRAQUAIR ON 
of the creature is correct, no matter on which side of it the openings supponay to be 
orbits are placed. 
No one will question the sensory nature of these openings, but that they really are 
eye-orbits, however possible or even probable that may be, is by no means certain. 
Their position is, however, analogous to that of the supposed orbits in Pteraspis ; and 
I can only repeat that, situated as they are so near to the right and left edges of the 
vertically flattened carapace, they might well, in the living and uncompressed condition 
of the animal, have enjoyed a considerable amount of lateral outlook. 
Scales of the tail-pedicle-—I have already in my previous memoir (p. 731) alluded 
to the fact that on that part of the tail which lies between the carapace and the caudal 
fin there is at least one longitudinal row of scales, which are considerably higher than 
broad, and which are seldom well seen, owing to that part being usually obscured by 
pyritous deposit. As the form of these scales can only be expressed in a direct lateral 
view, they could not be properly represented in my restored figures, in which the tail- 
pedicle is depicted as seen from above and from below. 
However, in fig. 2, Pl. Il. of this Supplement the tail-pedicle is seen free of pyrites, 
and here two. rows of such vertically elongated scales are clearly visible. At the caudal 
fin they pass into smaller scales of a rhombic form, which become very small on the 
fin-membrane. 
This specimen is also interesting in this respect, that, while lying on its ventral 
surface, that is to say, back upwards, the median dorsal plate has dropped out and the 
visceral aspect of the median ventral one has come into view, this plate being at once 
recognisable by the prominent emargination of its anterior border. This condition is 
the reverse of what more commonly occurs, for, as I have already stated, it is not at all 
rare to find in a specimen lying on its back that the median ventral plate has been lost, 
and the inner surface of the median dorsal one shown in consequence. See my previous 
memoir, Pl. [V., and explanation, p. 738. 
In sonclaein: I may remark that up to the present I have not been able to — in 
Drepanaspis any trace of a lateral sensory canal system. 
