Page:Synopsis of the Exinct Batrachia and Reptilia of North America. Part 1..pdf/16

12 DENDRERPETON, Owen.

Journal Geological Society, London, 1853, p. 81.

In the form of the cranium this genus differs from Brachydectes and cestocephalus much as Menopoma does from Amphiuma. Two species appear to have left their remains in the coal measures at Linton, Ohio.

There is an internal as well as an external suries of maxillary teeth in this genus, and a vomerine patch, according to Dawson. The skin was ornamented with osscous scales of an oval form, some of which were longer than others, and formed crest-like series along the side. In a specimen of the mandible of the D. acadianum, kindly sent me by Prof. Dawson, the inflection of enamel at the base of the tooth is readily observed, but it appears to be as smooth as in any other type of the Microsauria above the alveolar margin. Fig. 1.

DENDRERPETON OBTUSUM, Cope

This species is known by a partially preserved cranium. The superior surface is exposed, the outlines of the jaws and orbits are well preserved, with the occipital condyles. The os quadratum is directed obliquely backwards, and the angle of the mandible extends to a line a little behind that of the occipital condyles. The zygomatic arch exists in a position similar to that in which it may be seen in a few genera of Anura, as Discoglossus and Pelobates. It extends downwards and forwards from the supra-squamosal to the maxillary region, but whether it is homologically squamosal or malar the specimen cannot show. The postorbital is present as well, and with the last, and the supratemporal, forms the bony roof of the temporal fossa. A piece which may be the pre and post frontals combined, borders the inner superior margin of the orbit, it widens posteriorly, where it has contact with the parietal, etc., and narrows in front. Supraoccipitals form together a broad triangle on the upper plane of the cranium, of less extent than the adjoining supratemporal. These elements are pitted, and towards their margins radiate grooved. These sculpturings grow less on the margins of the supratemporal, and the portious of the surface of the more anterior elements remaining, are so slightly marked as to give the impression that the sculpturing in this species is much less than in others of the genus. A few beaded ridges are all that remain on the parietals and postorbitals; the maxillaries have a slightly stronger sculpture seen in a few spots.

The general form of skull is elongate behind, and much shortened in front of the orbits. The orbits are thus altogether in front of a line equally dividing the cranium transversely, while in the D. acadiauum they are in the middle of the skull. The outline of the muzzle in our species is then broad, rounded, as in the Menopoma alle- gheniensis, while in the latter it is ovate and produced. It therefore resembles also in its proportions the genus Herpetocephalus Huxl, from the Irish Coal Measures.

The parietal bones extend to opposite the posterior margins of the orbits, are then gradually contracted, and form an acuminate prolongation on each side the wedge-shaped frontals. The prefrontals are thickened on each side the front, behind the external nares. The sutures defining the frontals anteriorly, the nasals, and the premaxillaries behind cannot be made out. The median longitudinal suture is a marked and zigzag one, and can be seen as far