THE LOWER DEVONIAN FISHES OF GEMUNDEN,—SUPPLEMENT. A71 
‘is this aspect, represented in Pl. III. of my former memoir, which I have de- 
noted “ventral,” and on which we find two median plates, the anterior and 
smaller of which bounds the mouth behind, while the larger one has posteriorly 
a conspicuous median notch (cloacal), the direction of which is continued forwards 
for some little distance im the middle lie by the longitudinal fold to which I 
have already called attention. In this side of the creature are also seen the “ orbital” 
or sensory plates, the anterior and posterior ventro-laterals, and a narrow ex- 
ternal marginal portion of the postero-lateral on each side. In the specimen to which 
_ [have just referred the posterior extremity of the great median plate is deficient, but 
this deficiency I now remedy by figuring the one shown in Pl. I. of this Supplement, 
and I may say that this is the specimen which enabled me to complete the restoration 
of the plate in question, as seen in text-figure 3, p. 729 of my previous paper. Of this 
example an accurate photograph is given in PI. |. of the present communication, and on 
comparing this figure with Pl. III. (former paper) it will be at once seen that the 
creature presents to us the same oral surface ; for though the front part with the mouth 
is lost, there is no mistaking the “ orbital” of one side («.), the anterior ventro-laterals 
(a.v.l.), the postero-laterals (p.l.), and the posterior ventro-lateral of one side. In the 
centre of the specimen we see the great median plate (m.v.) of this surface, considered 
by me as ventral, in a state of nearly absolute completeness, though obliquely deformed 
like the rest of the specimen. With perfect clearness we see the bilobate front of this 
plate, the re-entering angle thereby formed being occupied by a portion of the mental 
plate (m.), while posteriorly the median fold, terminating on the notch behind, is shown 
with absolute distinctness. Then, below this, the hinder portion of the median plate 
(m.d.) of the opposite side is seen from its inner or visceral aspect, being brought into 
view by an oblique backward thrust. 
The aspect of the carapace to which the last-mentioned plate (m.d.) belongs is seen 
in Plates I. and II. of my former memoir. On it the mouth-slit is never visible, 
and consequently the term aboral may be temporarily applied to it. It shows 
only one large median plate, which differs strikingly from the corresponding one 
on the oral aspect in its proportionally narrower shape, in not being emarginate 
or bilobate in front, in having its posterior notch smaller, pointed in front and 
filled up by a narrow plate, and finally in the total absence of the median fold 
which is so conspicuous on the posterior part of the great median plate of the oral 
surface. We also recognise the aboral surface by the much greater extent to which 
the postero-lateral plates are visible, by the greater number of small polyoral plates 
surrounding the median one, by the fusion of some of these little plates into what I 
have called the rostral plates in front, and by the two shallow pits, one on each side of 
the front of the head, caused by the compression of one of the small plates over the 
ning-like thickening round the margin of the orbital or sensory opening internally. 
Having now made sure of the two surfaces of the carapace, the details of which are 
put together in my restored figures (pp. 726 and 729 of my previous memoir), it now 
