310 PROCEEDINGS OF THE GEOLOGICAL socieTy. [Apr. 19, 
in a slanting direction, from the front to the anterior part of plate a, 
would tell with most effect, and which had to be strengthened accord- 
ingly. It was at once a wall-plate to the roof above, and a rib 
directed from a strong groin towards the frontal part of that rhom- 
boid which the cuirass composed. He must have been no appren- 
tice workman who constructed the Pterichthys! Regarding the 
ventral superficies of the animal, 1 have only to remark, that the 
abdominal portions of the plates e, e, extended farther forwards 
towards the termination of the creature’s head or snout, than the 
dorsal plate a. 
“Two of my specimens indicate, Iam inclined to think, the place of 
the eyes. They were placed on the arched upper side, a little above 
the pomt at which the wings were inserted. The plates which covered 
this occipital part of the creature were small and numerous, not 
fewer than eight of them occurring in a space scarcely larger than 
that occupied by the central lhmpet-like plate. The creature’s wings, 
as shown by an unique specimen in my possession, were articulated 
to the body by a finely-formed ball and socket joint (fig. 2,1). I 
never met with any vestiges of teeth ; and infer, as I have now laid 
open many hundred specimens, that it had none. It bore on its tail 
a fin, like one of the two fins on the tail of the thornback, save that 
it was placed higher up, and had a small spme on its anterior edge ; 
and the minute scales with which this terminal part was covered 
were roughened with tubercles ranged more in lines than those of the 
plates. 
‘“‘Having in no specimen detected more than a single fin, I have 
made that fin a dorsal (Plate X. ) ; but there may possibly have been 
two opposite fins, as was supposed by the late Lady Gordon Cumming 
of Altyre; andif so, I would conclude that they were the creature’s ven- 
trals. The fringe or chevaux-de-frize (Plate X. 0), with the peculiarly- 
formed scale on its anterior edge, which runs to the point of the tail, 
oceurs on the same side as the fin. See, for evidence on this head, 
Agassiz’ figure, tab. 2. fig. 2,—evidence supported by all my speci- 
mens that bear on this point at all. This frmge seems to have been 
formed of peculiarlv-shaped scales. At one time I regarded it as the 
result of a chance grouping of the common scales seen in profile, but 
its invariable occurrence in the same place precludes the supposition ; 
and another supposition which I subsequently formed, that it was 
simply a protrusion of the processes of the vertebral column, proves 
equally untenable, as there existed on the spines tubercles indicative 
of external exposure. I possess two well-preserved specimens of the 
anterior scale : it was by far the strongest on the creature’s posterior 
extremity, pear-shaped, and fretted with mimute confluent tubercles 
arranged in longitudinal lines. 
“TI am afraid I can add nothing farther to my early deseription of 
the Pterichthys in my little work on the Old Red,—a description in 
which, though slight, I have not yet found much to amend. Agassiz 
figures, in his Monograph of the Fishes of the Old Red (tab. 30a, 
figs. 17, 18), a large hexagonal arched plate as the ventral centre- 
plate of Coccosteus maximus: from its appearance in the print, I 
