ORDER I STEGOCEPHALIA 1 1 7 



the sakral ribs, and is directed obliquely downward ; a flattened, sometimes 

 discoidal bony ischium ; and a cartilaginous or ossified pubis lying imme- 

 diately in advance of the ischium. The ilium and ischium usually take part 

 together in the formation of the acetabulum, which receives the femoral head. 

 In the Anura the tibia and fibula are fused. The tarsus is cartilaginous or com- 

 posed of several small ossicles, and the pes resembles the manus, except that 

 it is usually pentadactyle. 



Four Orders of Amphibians are recognised as follows : — Stegocephalia, Gymno- 

 phiona, Urodela, and Anura. 



Order 1. STEGOCEPHALIA.^ 



Salamander or lizard-Uke caudate amphibians, the cranial roof and whole of the 

 cheek covered with plates ; cranial roof posterior to the orbitsformed by two pairs of 

 median and two pairs of lateral elements ; pineal foramen always occurring in the 

 parietal. Teeth sharply conical, with large pulp cavity, and walls sometimes highly 

 complicated by infolding of the dentine. Vertebrae consisting either of simple 

 cylinders, or of separate pleurocentra and hypocentra, or of completely ossified amphi- 

 coelous centra. Three exoskeletal plates present in the thoracic region, interpreted 

 as clavicles and interclavicle. Usually a ventral and som,etimes a dorsal armouring 

 of small overlapping scales. 



The Stegocephalians ränge from the Carboniferous to Upper Trias, 

 and comprise the largest known amphibians. A tail is invariably present, and 

 in most cases, two pairs of limbs ; only a few genera are apparently destitute 

 of appendages. 



Unlike recent amphibians, most Stegocephalia possess a well-develbped dermal 

 armour of bony scales or scutes, which almost always Covers the ventral sur- 

 face of the body, and sometimes extends to the under side of the limbs and 

 back as well. Dorsal scales, however, are thinner than the abdominal, and 

 are usually round or oval. The ventral scutes are sometimes thickened, and 

 always arranged in regulär series. The abdominal series form oblique rows 

 meeting at a sharp angle along the median line, but those covering the 

 thoracic, pectoral, and caudal regions, and under side of the limbs are arranged 

 in difFerent patterns. The scales are of true bony tissue, and vary considerably 



^ Literature : 



Amnion, L. v.. Die permischen Amphibien der Rheinpfalz. Munich, 1889. [Extensive biblio- 

 graphy. ]— 5a?^r, O., The Stegocephali : a Phylogenese Study (Anat. Anz. vol. XI. No. 22), 1896.— 

 Broüi, F., and Stickler, L., lieber Eryops megacephalus Cope (Palaeontogr. vol. XLVI.), 1899.— 

 ßm-meister, II., Die Labyrinthodonten aus dem bunten Sandstein von Bernburg. Berlin, 1840.— 

 Die Labyrinthodonten aus dem Saarbrücker Steinkohlengebirge. Berlin, 1850. — Cope, E. D., 

 Synopsis of the extinct ßatrachia and Reptilia of North America (Trans. Amer. Phil. Soc. vol. 

 XIV.), im^.—Ibid. N.S., vol. XVI., 1886.— Batrachia of the Permian Period of North America 

 (Amer. Nat. vol. XVIII.), \%d>i.—CredneT, H., Die Stegocephalen aus dein Rothliegenden bei 

 Dresden. Parts I.-X. (Zeitschr. deutsch, geol. Ges.), 1881-93. — Fraas, E., Die Labyrinthodonten 

 der schwäbischen Trias. (Palaeontogr. vol. XXXVI.), 1889.— ^r/for/;, .4., Die Fauna der Gaskohle 

 und der Kalksteine der Permforniation Böhmens, vols. I.-IIL, 1883-94. — Hiixley, G. ^., Vertebrate 

 Remains from Kilkenny (Trans. Roy. Irish Acad. vol. XXIV.), 1867. — Jaekd, 0., Die Organisation 

 von Arehegosaurus (Zeitschr. deutsch, geol. Ges. vol. XLVIIL), 1896. — lieber die Körperform und 

 Haut l»edeckung von Stegocephalen (Setzber. Ges. naturf. Freunde, Berlin), 1896. — Meyer, H. v., Zur 

 Fauna der Vorwelt, pt. 2, Frankfort, 1847. — Ueber den Arehegosaurus (Palaeontogi-. vols. I., VI. 

 XV.), 1851, 1857, 1866. — Idevi, and Plienenger, T., Beiträge zur Palaeontologie Württembergs. 

 Stuttgart, 1844. — Miall, L. C, Report on the Structure and Classification of the Labyrinthodonts 

 (Rept. Brit. Assoc, 42nd and 43rd Meet.), 1874-75. 



