﻿28 GANOID FISHES OF THE CARBONIFEROUS FORMATION. 



overlapped by the joint in front, and behind this line the surface is free, ganoid, and 

 sculptured. On the internal aspect there is a vertical keel, also resembling the keel on 

 the inner aspect of a scale, and which, when all the joints of a demi-ray are in apposition, 

 forms with its fellows above and below a long ridge, and the groove between two such 

 ridges may have been mistaken by Agassiz for the impression of an internal ray 

 when seen in the entire fin of one of the smaller species, the set of demirays next the 

 observer having been partially removed. The resemblance between the articles of the 

 rays, when seen from the outer surface, and the scales of the body, is sometimes extremely 

 deceptive, especially in some forms of Amblypterus, e. g. A. lepidurus, A. (?) Blainvillii, 

 which were referred to by Agassiz as examples of Palaoniscus, with scaly covering to 

 their fins, while in Bhabdolepis macropterns and Palaoniscus Freieslebeni he did not con- 

 sider such a covering to exist. Nevertheless, I see no evidence in any case, that anything 

 is shown on the outside of the fins but the ganoid surfaces of the joints of the rays 

 themselves, as in the fins of the recent Lepidosteus and Polypterus, in which certainly no 

 scaly covering apart from the rays exists. 



The anterior margins of all the fins are in most (if not all) of the Palaoniscida orna- 

 mented with the little pointed imbricating scales, or accessory raylets, known as "fulcra." 

 These follow immediately on the prominent azygous scales seen in front of the fins in 

 most genera, and may frequently be seen to be at first intercalated between the extremities 

 of the first short rays, and, as these elongate, form a more continuous series impinging on 

 the ray at acute angles. Whether these fulcra form a single or double series is a point 

 very difficult to determine accurately, seeing that in almost every case the fin is 

 seen only from the side. If we consider the V-shaped scales along the upper 

 margin of the caudal body prolongation to be " fulcra" (though I prefer to class these 

 with the body-scales), they are in this case undoubtedly single, where their form is 

 distinctly seen, save in Cheirolepis, where the legs of the V are divided at the point of 

 meeting. But as regards the lower lobe of the caudal, and the same would 

 doubtless hold good as to the other fins, they were believed by Midler to be double 

 in Acrolepis and Palaoniscus, an opinion concurred in by Martin, and which is 

 extremely probable to be the correct one, although I have not myself seen any absolutely 

 clear demonstration of the fact. 1 I cannot, however, see that any very great systematic 

 importance can be attached to the monostichous or distichous arrangement of the fulcra, 

 or, indeed, to their total absence. No fulcra have been observed in Cosmolepis or 

 Thrissonotus, or any other fins save the caudal ; but, though they have been considered 

 to be similarly absent in Oaygnat/tus, I have detected them on both the dorsal and pectoral 

 fins in that genus. In most Palceoniscida the fulcra are very small ; sometimes, as in 

 Bhabdolepis, so minute that they can only be made out by very careful examination ; they 

 are, however, prominent enough in Acrolepis, Pygopterus, and Centrolepis. 



1 Since the above lines have been in type I have succeeded in finding undoubted evidence of the 

 distichous arrangement of the fulcra in the anal fin of an Elonichthys from the north of Ireland. 



