CLASS 11.—REPTILIA.
Order I.—OANOCEPHALA..
The name of this order has reference to the sculptured and externally polished or " ganoid " bony plates with which the entire head was defended. These plates include the " post-orbital " and " super-temporal" ones, which roof over the temporal fos&e. There are no occipital con dyles. The teeth have converging inflected folds of cement at their basal half. The notochord is persistent ; the vertebral arches and peripheral elements are ossified; the pleurapophyses are short and straight. There are pectoral and pelvic limbs, which are natatory and very small ; large median and lateral " throat-plates ;" scales small, narrow, sub-ganoid ; traces of branchial arches. The above combination of characters gives the value of an ordinal group in the cold-blooded Vertebrata.
Genus APATEON, Von M. ; ARCHEGOSAITRUS,t Gold£ The extinct animals which manifest the above ordinal characters were first indicated by certain fossils, discovered in the sphxrosideritic clay-slate forming the upper member of the Bavarian coal measures ; and also in splitting spheroidal con cretions from the coal-field of Saarsbruck, near Treves. They were originally referred to the class of fishes (Pygopterus Lucius, Agassiz) : but a specimen from the Brandschiefer of Munster Appel presented characters which were recognized by Dr. Gergens to be those of a salamandroid Dr. Gergens placed his "sala mander" in the hands of H. von Meyer for description, who communicated the result of his examination in a later number of the under-cited journal.t In this notice the author states that the sala mandroid affinities of the fossil in question, for which he proposes the name of A pateon pedestris, " are by no means demonstrated:1 " Its head might be that of a fish as well as that of a lizard, or of a Batrachian." " There is no trace of bones or limbs." M. von Meyer concludes by stating that, in order to test • Mainz, Oktober 1843. " In dem Brandschiefer von Munster appel in Bkein-Baier% habe ich in vorigen Jahre einen Salamander sufgefunden. Gehort dieeer Schiefer der Kohlen-formation? in diesem fah, ware der Fund ouch in anderen ifinsicht interessant." (Leonhard and Bronn, Nemo Jahrbuch fur Mineralogie, etc., 1844, p. 49.)
f Ibid, 1844, p. 336.
Three years later, better preserved and more instructive specimens of the problematical fossil were obtained by Pro fessor von Dechen from the Bavarian coal-fields, and were submitted to the examination of Professor Goldfuss of Bonn : he published a quarto Memoir on them, with good figures, referring them to a saurian genus which he calls Arekego saurus, or primaeval lizard, deeming it to be a transitional type between the fish-like Batrachia and the lizards and crocodiles.* The estimable author, on the occasion of publishing the above Memoir, transmitted to me excellent casts of the originals therein described and figured. They are in the museum of the Royal College of Surgeons, and are described in my Catalogue of the Fossil Reptiles, 4to, 1854, p. 117.t One of the specimens appeared to present evidence of persistent branchial arches. The osseous structure of the skull, especially of the orbits, through the completed zygo matic arches, indicated an affinity to the Labyrinthodonts ; but the vertebra and numerous very short ribs, with the indications of stunted swimming limbs, impressed me with the conviction of the near alliance of the Archegosaurus with the Proteus and other perennibranchiate reptiles.
This conclusion of the affinity of Archegosaurus to existing types of the reptilian class has been confirmed by subse quently-discovered specimens, some of which have been acquired by the British Museum, others have been described and figured by H. von Meyer in his Palccontographica vi., 2to Lief. 1857) ; more especially by his discovery of the embryonal condition of the vertebral column—i. e., of the persistence of the notochord, and the restriction of ossification to the arches and peripheral vertebral In this structure the old carboniferous reptile resembled the existing Lepidosiren, and affords further ground for regarding that remarkable existing animal as one which obliterates the line of demarcation between the fishes and the reptiles.