Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/652

552

The species referred to Amblypterus in the "Poissons Fossiles" certainly fall into at least five distinct types:—

I. Type of A. latus, Ag. (Genus Amblypterus, Ag., restricted). The body is rather deep; the scales smooth; the fins large and many-rayed, with minute fulcra; the dorsal placed a little further back than in the next type; the caudal powerful. The suspensorium is not so oblique as in the Palæoniscidæ in general; hence the position of the operculum is more vertical, and the gape proportionally less extensive. There is no small plate (suboperculum) intercalated between the operculum and the interoperculum. The teeth are minute and very slender; there are no large conical laniaries; hence the term "en brosse" is here more applicable than in any other genus of Palæoniscidæ.

To this type the title Amblypterus should be strictly limited as recommended by Troschel; but I must also add that I am unable to see any tangible grounds of distinction between these forms and the smooth-scaled Palæoaisci of the type of P. Duvernoyi, whose reception into the genus Amblypterus is therefore to be recommended. To this point I shall, however, return further on under Palæoniscus. A. latus and lateralis are characteristic fossils of the Lower Permian strata of Saarbrücken and Lebach; and the other species, which I propose to unite with them generically, also occur in strata of similar age in Germany, Bohemia, and France; so that Amblypterus must be deleted from the list of Carboniferous genera, in spite of the length of time during which geologists have been accustomed to look upon it as one of the characteristic forms of the Coal-period.

II. Type of A. macropterus, Ag. (Genus Rhabdolepis, Troschel). The scales are moderate, finely striated; the fins large, many-rayed, with minute fulcra; the dorsal placed nearly opposite the interval between the ventrals and the anal, the base of the ventrals not specially extended; the caudal powerful. In each jaw there is a row of stout conical laniary teeth, external to which is a series of smaller ones. The dentition, thus quite conformable to that in Acrolepis or Pygopterus, would alone be sufficient to demand the separation of these forms from the true Amhlypteri; but careful examination reveals still further differences in the structure of the head. The suspensorium is very oblique, the operculum small; and between it and the square-shaped plate hitherto considered as "suboperculum," but which I have now come to look upon as interoperculum, there is another of a narrower form (suboperculum).

For fishes of this type, which have as yet only occurred in strata of Lower-Permian age, the genus Rhabdolepis of Troschel must be maintained. The presence of the subopercular plate distinguishes this genus from Elonichthys of Giebel, the form and extent of that plate as well as the shorter base of the ventral fins from Cosmoptychius (mihi).

III. Type of A. striatus, Ag. (Genus Cosmoptychius, Traquair).