Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/665

Rh opposite side; there is no trace of any infraclavicular, so constant and prominent an element in the shoulder-girdle of all the Palæoniscidæ.

The scales of the body are smooth ; and those of the flank remind us, in their form, more of the scales of Pholidophorus than of Palæoniscus.

These details render it sufficiently evident that the fishes entitled, by Mr. Kirkby, Palæoniscus varians, Abbsii, and altus belong neither to the genus Palæoniscus, nor even to the family of Palæoniscidæ. The differences of structure between them and all the other genera which may be included in the last-named family are, indeed, so strong that I am a little surprised to find him comparing Palæoniscus varians with such forms as P. Voltzii, angustus, and wratislaviensis—species which, if they cannot be included in the genus Palæoniscus as now restricted, most obviously belong to the Palæoniscidæ. Palæoniscus fultus and P. glaphyrus are also mentioned as allied, especially the latter; and here I am able most fully to agree with the author; for P. glaphyrus seems, indeed, to be closely related to, if not generically identical with, the little fishes in question. But if that be the case, then it also, as already mentioned, must cease to be regarded as having even family relations with Palæoniscus. But, as regards Palæoniscus fultus, Mr. Kirkby seems to have overlooked the fact that as far back as 1847 it was transferred by Sir Philip Grey-Egerton to a new genus, namely Ischypterus; and I have above shown how widely this genus differs from the Palæoniscidæ in most essential points of structure. It is, in fact, not the type of Palæoniscus, but that of Lepidotus and its allies, which rises before the mind on the contemplation of the structural details of these fishes along with their entire aspect. And it is precisely with this American genus Ischypterus that Mr. Kirkby's fishes display the greatest possible affinity—in the structure of the tail, of the fins, and in the osteology of the head, so far as that can be made out in the genus just named. A difference of decided generic value, however, is to be found in the absence, in the Fulwell-Hill fishes, of the median row of spur-shaped scales along the back, so prominent in Ischypterus; and in reference to this distinction, I propose the new generic term Acentrophorus for the Palæoniscus varians, Abbsii, and altus of Kirkby. Whether or not Palæoniscus glaphyrus of Agassiz is also inclusible in this genus, can only, as aforesaid, be accurately determined by a reexamination of the type specimen; but that it also is not related to the Palæonisci is meanwhile pretty clear to my mind.

VII. Type of Palæoniscus catopterus, Ag. (? Genus Dictyopyge, Egerton). This little species, from the Triassic Red Sandstone of Phone Hill, co. Tyrone, was originally named by Agassiz, but was not described by him. Sir Charles Lyell, however, in referring to it in connexion with certain American Triassic forms, says concerning it:—"The Irish Palæoniscus catopterus of Roan or Rhone Hill, referred by Col. Portlock to the Trias, is a true Palæoniscus, and not allied generically either to the Ischypterus of Egerton or the