230 PERMIAN FOSSILS. 
proposed, whether they should be referred to the tegumentary investment, or to the 
internal skeleton of the fish. Agassiz advocates the latter theory, and recognises in 
them the analogues of the V-shaped bones in the Clupee. My reasons for thinking 
otherwise are as follows. In the first place, these so-called apophyses are traceable from 
the back to the belly, external to the vertebral column and true apophyses; secondly, 
they are comcident with the dorso-ventral series of scales; and thirdly, they are 
united to—not articulated with—the external spines or scales in front of the dorsal 
fin. If we examine the scales of the Pycnodonts, we shall find that they all agree in 
the mode of articulation, viz. in having a thick solid projecting rib on the inner 
anterior margin, sliced off above and below on opposite sides for forming splices with 
the similar processes of the adjoining scales. These splices are so beautifully adjusted, 
that without a magnifying power or an accidental dislocation, they are not perceptible. 
When zz si¢u and seen internally, these continuous lines decussate with the vertebral 
apophyses, and cause the regular lozenge-shaped pattern so characteristic of the 
Pycnodonts. The Ferry-Hill specimen of Platysomus, and some beautiful Gyrodh, - 
which I owe to the kindness of the late Count Minster, demonstrate that, as far as 
these genera are concerned, this is the correct solution of the problem. 
Platysomus macrurus seems to have been a more robust fish than its nearest ally, 
P. striatus. The distinctive characters of the tail and the position of the fins have 
been well noted by Agassiz. The fin rays in this species are much stronger, and the 
transverse articulations more frequent. They are composed of two distinct substances, 
an inner bony tissue of dark colour, and an outer layer of hard enamelled substance 
similar to the ganoine of the scales. It is of much lighter colour than the subjacent 
bone, and translucent. The joints are coincident with those of the inner core, and 
the surface is neatly sculptured with transverse furrows. The anterior rays of the 
dorsal fin are supported by a series of strong flattened plates, considered by Agassiz 
to be sur-apophysary, rather than inter-apophysary bones. The ventral fins, so rarely 
preserved in this genus, are situated a little in advance of the insertion of the dorsal 
fin, rather nearer to the pectoral than the anal fin. The dorso-ventral series of scales, 
from the nape to the belly, make an elegant sigmoid flexure. The scales themselves 
are thicker than those of P. striatus, and the ornament on their surface more strongly 
marked, especially in the anterior part of the body. The processes by which the 
scales are interlocked, form, when 7 situ, the remarkable ridge discussed in the former 
part of this article. ‘The outer surface of the flanks in this species seems to have 
been deeply fluted, in lines parallel to the dorso-ventral series of scales, at least such 
is the character of the impression seen in places where the scales are wanting. It is 
probable, from the small size of their oral aperture and the characters of their teeth, 
that the P/atysom: fed either on marie plants or small shell-fish; and we see in their 
dense tegumentary investment, a means of protection against the aggressions of their 
more rapacious contemporaries ; but, that even this was sometimes ineffectual we have 
