230 PERMIAN POSSILS. 



proposed, whether they should be referred to the tegumentary investment, or to the 

 internal skeleton of the fish. Agassiz advocates the latter theor)'', and recognises in 

 them the analogues of the V-shaped bones in the Clupea. 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 coincident 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 ofi' 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 in situ 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 Plati/somus, and some beautiful Gyrodi, 

 which I owe to the kindness of the late Count Mlinster, demonstrate that, as far as 

 these genera are concerned, this is the correct solution of the problem. 



Platyso7nus macrurus seems to have been a more robust fish than its nearest ally, 

 P. striahis. 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. striaius, 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 in 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 pai'allel 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 Platysoini fed either on marine 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 



