A. _Perennibranchiata_, whose chief distinguishing skeletal characters are that the skull is elongated, the premaxillae are not ankylosed, the maxillae are vestigial or absent; there are sometimes no nasals, and the palatines bear teeth; e.g. _Siren_, _Proteus_, _Menobranchus_. B. _Derotremata_, whose chief distinguishing skeletal characters are that there are large maxillae and nasals; teeth are borne by both maxillae and premaxillae; there are no palatines; and both pectoral and pelvic limbs are always present; e.g. _Amphiuma_, _Megalobatrachus_, _Cryptobranchus_. _Suborder_ (2). SALAMANDRINA. The vertebrae are opisthocoelous. The skull is broad, and teeth are borne by both premaxillae and dentaries. Nasal bones are present. The remains of only two branchial arches are found in the adult. The carpus and tarsus are more or less ossified. This suborder includes the Newts (_Molge_), Salamanders (_Salamandra_), and _Amblystoma_. _Order_ 2. LABYRINTHODONTIA[52]. These are extinct Amphibia with a greatly developed dermal exoskeleton, which is generally limited to the ventral surface. The body and tail are long and in some cases limbs are absent. The teeth are pointed and often have the dentine remarkably folded. The vertebrae are amphicoelous, and are generally well ossified. The skull is very solid, and has a greatly-developed secondary roof which hides the true cranium and is very little broken up by fossae. Paired dermal supra-occipitals are found, and there is an interparietal foramen. The epi-otics and opisthotics form a pair of bones distinct from the exoccipitals. Four simple limbs of moderate length are generally present, and in some cases all four limbs are pentedactylate. Among the better known genera of Labyrinthodonts are _Mastodonsaurus_, _Nyrania_, and _Archegosaurus_. _Order 3._ GYMNOPHIONA[53]. These animals form a group of abnormal worm-like Amphibia having an exoskeleton in the form of subcutaneous scales arranged in rings. The vertebrae are biconcave and are very numerous; very few however belong to the tail. The skull has a complete secondary bony roof, the mandible bears teeth and has an enormous backward projection of the angular. The hyoid arch has very slender cornua and no distinct body, it is attached neither to the cranium nor to the suspensorium. The ribs are very long and there are no limbs or limb girdles. _Order 4._ ANURA. These are tailless Amphibia, which except in a few instances, are devoid of an exoskeleton. The vertebrae are as a rule procoelous, and are very few in number. The post-sacral part of the spinal column ossifies continuously, forming an unsegmented cylindrical rod, the urostyle. Remains of the notochord persist, lying _vertebrally_, i.e. enclosed within the centra of the several vertebrae, and not as in Urodela lying between one vertebra and the next. The skull is very short and wide. The mandible is almost always, if not invariably, toothless.