Dr. R. H. Traquair—Homosteus and Coccosteus ‘compared. 7 
supposed “hyoid,” that it requires no further description, beyond 
the remark that its resemblance to that of Coccosteus, except in its 
short broad shape and the want of the posterior elongated peak, 
must be evident at the first glance. It is here shown in position, its 
broad margin being directed forwards, and lying parallel to the 
posterior margin of the cranium, from which it is here separated 
by a narrow gap, its obtuse point being free and posterior. Its 
lateral margins overlap on each side two other bones, of which the 
anterior one (a. d. 1.) was figured by Hugh Miller as “non-descript 
latero-hyoidal plate,” he being well aware of its relation to the 
median bone, though, in accordance with his theory of the latter, 
he reversed its position. Its relation to the skull was, however, 
correctly represented by Pander (‘‘ Placodermen,” tab. 8, fig. 2a.). 
Jt consists of two parts, one flattened above, and applied anteriorly 
to the outer part of the posterior margin of the skull, by which as 
well as by the median plate it is overlapped, and another, narrower, 
forming a right angle to the flattened portion and running forwards 
a little way along the posterior part of the outer margin of the 
cranial buckler; in the angle between the two parts is a socket for 
articulation with a corresponding projection of the postero-external 
angle of the external occipital. Naturally Hugh Miller found him- 
self at a loss to account for the presence of this socket. Different 
as the two bones are in shape, it is impossible not to recognize in 
this bone the homologue of the anterior dorso-lateral in Coccosteus 
(Fig. 3), though here the socket and peg have changed their positions 
on the bones concerned. 
Behind this anterior dorso-lateral there exists in the specimen 
figured in Pl. I. Fig. 1, another and much smaller plate (yp. d. I.) 
on each side, which has not previously been noticed. It needs no 
reasoning to perceive at once that this is the posterior dorso-lateral 
of Coccosteus (p. d.1., Fig. 3). 
It is curious that no undoubted remains of a ventral body-carapace 
like that of Coccosteus have occurred in connection with Homosteus ; 
but, at the same time, I might mention that the plate (Footprints, 
fig. 37) designated “palatal plate” by Hugh Miller, looks to me as 
if it might well be the anterior median ventral, so far as its shape 
is concerned, though its great size may be considered as somewhat 
against the supposition. At all events there is no evidence for 
referring it to the palate. 
There are also several other bones figured by Hugh Miller and 
contained in the Edinburgh Museum, which from the way in which 
they occur, associated with other undoubted remains of Homosteus, 
clearly belong to the same fish, but whose position in the body I 
cannot speculate upon. ‘These are the “operculum” (Footprints, 
oth edition, fig. 39), the very curious bone (ib. fig. 43) spoken of by 
Hugh Miller, as “shoulder (i.e. coracoid?) plate”; his so-called 
“dermal bones” (ib. fig. 44). What the bones ¢ and e in fig. 46 
of the “‘ Footprints ” are I am also unable to determine. 
But a number of the other remains figured in the “ Footprints ” 
as “ Asterolepis” belong not to Homosteus, but to Glyptolepis 
