AMPHIBIA. URODELA. 135 



The Ichthyoidea may be subdivided again into two 

 groups : 



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 cha- 

 racters are that there are large maxillae and nasals \ teeth are 

 borne by both maxillae and premaxillae ; there are no pala- 

 tines ; and both pectoral and pelvic limbs are always present ; 



e.g. Amphiuma, Megalobatrachus, Cryptobranclm-s. 



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 1 . 



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 



1 See A. Fritsch, Fauna der Gaskohle, Prague, 1883-85-86, also writings 

 of Cope, Credner, Huxley, H. v. Meyer, Miall. 



