Catopterus of Redfield"[1]. And in Sir Philip Grey-Egerton's brief description of the species[2] occurs the following passage:—"The dorsal fin is placed much nearer the tail than in any other species; in this respect, but in no other, Palæoniscus catopterus resembles the genusCatopterus of Mr. Redfield. The tail is decidedly heterocerque." The eye is also said to be placed forwards, the mouth to appear small, the operculum to be nearly semicircular.
The smallness of the mouth would in itself be considerable presumptive evidence against the affinity of this species with Palæoniscus, in which the gape is enormously extensive, as it is also, more or less, in the entire family; it displays, however, another peculiarity which conclusively shows that the position hitherto assigned to it is incorrect.
However, the specimens usually seen in collections are almost always in so bad a state of preservation, from their very friable nature, that it is not astonishing that such eminent naturalists as Agassiz, Lyell, and Grey-Egerton should have fallen into error as regards its affinities; indeed they are ordinarily so rubbed and abraded that in many cases it is barely possible to determine that they are the remains of small ganoid fishes. But in the Museum of Practical Geology, Jermyn Street, there is one rather good specimen, and in the collection of the Geological Survey of Ireland there are several others, on examining which I was not a little surprised to find that the tail is not that of Palæoniscus. The fin-rays are, as in the Palæoniscidæ, closely set and articulated throughout, their fulcra being small and numerous; and the tail is deeply cleft and somewhat inequilobate. But the body-scales stop short in a little rounded "sinus," which projects only a very short distance up into the base of the upper lobe of the caudal fin, and is then followed by rays which are just as elongated as those of the lower lobe. The tail is therefore much less heterocercal than in Ischypterus or Acentrophorus, in fact not more so than in Lepidotus; so that the retention of this little fish in the family Palæoniscidæ is no longer possible.
Are we, however, to consider it as the type of a new genus, or can it be received into any previously known? This question can only be answered to complete satisfaction when fresh specimens are discovered from which the structure of the head can be more fully made out; and, unfortunately, since the first "find," none have come to light either in the original or in any other locality. Meanwhile, if we turn to the figure of Dictyopyge macrura (Catopterus macrurus, W. C. Bedf.), from the Virginian Triassic strata, given in the previously quoted memoir by Sir Charles Lyell, we shall find that there is a very obvious correspondence between it and the Rhone-Hill fish in the form of the tail, and in the structure and position of the fins—so much so that the probability of their belonging to the same genus seems to me very great. Still greater is the resemblance which it bears to the Dictyopyge socialis of
