Of these one must be deleted before proceeding further, viz. P. Indus, from Saarbrücken, which subsequently turned out to be a head of Archegosaurus[1]. Of two others I can give no account, viz.:—P. Bonnardi, from the Autun fish-beds (now referred to the Lower Permian), which I have never seen, nor am I aware of its having ever been described; and P. Jamesonii, from Burdiehouse, of which also no description has ever appeared; and as the specimen, a detached jaw, appears to be lost, the name must be cancelled, like too many others given by Agassiz to fish-remains to whose identification we have no longer any clue. The others fall into the three following generic types.
I. Type of P. Humboldtii (genus Pygopterus, Agassiz, restricted).—The general form is elongated; the head is rather large, the suspensorium very oblique; the jaws long, powerful, and armed with large conical laniaries, outside which is a series of smaller teeth; the operculum and interoperculum are rather small, the branchiostegal rays numerous; both the cranial and facial bones are striated. The scales of the body are small in proportion to the size of the fish, nearly equilateral over the greater part of the body, but rather higher than broad on the front of the flank; their form is rhomboidal, their anterior marginal covered area is moderate, and at the anterior superior angle of the scale is produced upwards into a prominent point; the proper articular spine of the upper margin is well marked. The pectoral fin is of considerable but not excessive size; its principal rays are, like those of Oxygnathus and Rhadinichthys, unarticulated till towards their terminations; the ventral is rather small. The anal commences rather remote from the caudal; it is high and acuminate in front; but behind the apex its contour falls rapidly away, so that posteriorly it extends in a fringe-like manner for some distance along the lower margin of the body. The dorsal commences slightly in front of the anal, and has a much shorter base, the middle of which is opposite the commencement of the last-named fin; it is acuminate and high in front, the posterior margin being concavely cut out. The caudal is of enormous size, powerfully heterocercal, deeply cleft, but not very inequilobate. The fin-rays do not seem to me to have been ganoid externally, but to have been covered with a delicate skin, as in the recent Polyodon; the fulcra are well marked. The internal skeleton is well developed, the vertebral arches, spinous processes, and interspinous bones usually showing prominently through the external scaly covering; but it seems to me very doubtful that the vertebral bodies had got beyond the stage of "Halbwirbel:" nor have I seen any trace of ribs, though these are mentioned by Germar. The snout projects over the front of the mouth, as in other Palæoniscidæ; hence, probably, the expression used by Agassiz:—"La mâchoire supérieure déborde l'inférieure."
- ↑ Dr. G. Jäger, "Ueber die Uebereinstimmung des Pygopterus lucius, Ag., mit dem Archegosaurus Dechenii, Goldf.," Abh. der k.-bayerisch. Ak. der Wiss. v. pp. 877–886. See also a notice by Prof. Ferd. Römer, in Verh, preuss. Rheinl. u. Westphal. 1850. pp. 155–157.
