Fossil Fishes of the Upper Old Red Sandstone. 379 
of which I have represented a small portion in Pl. XI, 
Fig. 5, magnified two diameters. The small polygonal 
areas into which the outer layer of the shield is divided, 
and which correspond to shallow depressions of similar 
form on the outer surface of the middle layer, are here 
very distinctly seen. The surface of each of these areas 
is slightly convex, and closely covered with stellate tubercles, 
In or near the centre of each area is a tubercle usually larger 
than the others, which tend to be arranged round it in a 
more or less concentric manner. The vertical thickness of 
this fragment is } inch. 
Psammosteus pustulatus, sp. nov., Traquair. 
[Plate XI., Figs. 3 and 4.] 
In my “Extinct Vertebrata,’ I mentioned the fact that 
small fragments of plates apparently belonging to Psammosteus 
had been found at Scaat Craig by Mr Taylor, in addition to 
the fragment of a “spine,” which I figured from the collec- 
tion of Mr Grant of Lossiemouth. I had also found, on an 
excursion which I made with Mr Taylor to the same locality, 
a similar fragment, which, when subsequently extracted en- 
tirely from the matrix, showed clearly on the outer surface 
the abraded remains of a Psammosteus-like tuberculation. 
Subsequently I found much better pieces in the Brickenden 
Collection in the British Museum, one of which (Pl. XL, 
Fig. 3) I have adopted as the type of a new and very 
distinct species. 
These fragments are water worn at the edges, and generally 
abraded on the surface; when broken across, their internal 
structure is that of Psammosteus so far as can be seen with 
a good lens, as I have not yet obtained any section sufficiently 
thin for examination with a high power. The outer surface 
shows in most cases only the worn stumps of rounded 
tubercles, which are proportionally large, attaining a diameter 
at the base of ,4, to; inch. In the specimen represented 
