THE LOWER DEVONIAN FISHES OF GEMUNDEN,—SUPPLEMENT. A73 
lobe of the caudal fin in the Angel-fish (Squatina) is larger and projects further back 
than the dorsal one, there is no downward bend of the vertebral axis, which proceeds 
straight backwards. Nor has the greater size of the lower caudal fin lobe in the 
teleostean homocercal Flying-fish (Hxocetus) any bearing on the question. 
Another circumstance which cannot be overlooked is the position of the mouth. 
This, as I have already shown, is not truly terminal, but is situated on that aspect of 
the carapace which is coincident with the shorter margin of the fin and the apparent 
eloacal opening. Now, although the mouth may appear to look upwards in such a 
peculiarly specialised bony fish as the recent Angler (Lophius), yet, judging from the 
analogy of other Ostracoderm types, such as Pteraspis, Cephalaspis, and Asterolepis, 
the dorsal side is not the one on which we would expect to find it in the case of 
Drepanaspis. 
But of really crucial importance is the position of the cloacal opening or vent. It, 
at least, we cannot expect to find on the dorsal aspect of the tail of a fish or fish-like 
vertebrate, unless we should take upon ourselves to deny the presence of a notochordal 
vertebral axis in those creatures. Now if we look at Pl. II. of my former memoir, which. 
represents the aboral surface of the fish, we find no trace of any such opening, although 
the scales of the middle line, between the posterior margin of the great median plate 
and the fulcra of the tail, are in complete order and well preserved. The aboral side 
of the fish is therefore not ventral; and if it be not ventral, then it is dorsal, and the 
oral side is the ventral one, in accordance with my original description. 
Turning now to this oral side,—in the specimen represented in fig. 1, Pl. V. of my 
former memoir, the position of the cloacal opening seems to me to be distinctly marked 
just in the notch which follows the prominent posterior median fold of the great central 
plate, in front of the first fulcral scale in the middle line. Again, in the specimen 
represented in Pl. III. of the present Supplement, we have the great median plate 
(m.v.) of the aboral surface distinctly shown, as is also its median fold behind and the 
notch ¢., though one margin of the latter is broken away. It is this notch c. which, in 
my opinion, marks the position of the cloacal opening, in perfect accordance with the 
appearances shown in the figure just referred to, and also represented in the restoration 
of the ventral surface in text-figure 3, p. 729 of my previous memoir. It is, however, to 
be noted that in this specimen (PI. III.) the anterior extremity of the first (ventral) 
fuleral scale is slightly displaced, or shoved to one side, so that it no longer closes the 
cloacal notch (c.), which is consequently left open behind. 
I submit, therefore, that I have amply shown— 
First.—That the aboral aspect of the carapace of Drepanaspis is coincident with 
the apparent dorsal “lobe” or aspect of the caudal fin. 
Second.—That the absence of a cloacal opening on the aboral aspect of the 
commencement of the tail, and its apparent presence on the oral one, is equivalent to a 
proof that the aboral margin of the tail, consequently of the entire creature, zs the 
dorsal aspect. Conversely, the oral aspect is the ventral; and my previous orientation 
