URODELA. 347 



Ophiomorpha, Urodela, Anoura,d.ndiLabyrinthodontia. The first 

 of these includes only the serpentiform animals known as 

 Ccealia, and not having any certain fossil representatives, may 

 be altogether passed over here. The order Urodela comprises 

 the so-called " tailed " Amphibians of the present day, such as 

 the Newts and Salamanders. The earliest traces of this order 

 in past time occur in the Tertiary deposits. The order Anoura 

 includes the so-called " tail-less" Amphibians, such as the Frogs 

 and Toads, and is likewise not known to have existed in periods 

 anterior to the Tertiary. Lastly, the order Labyrinthodontia 

 is entirely extinct, and is known to have existed only during 

 the Carboniferous, Permian, and Triassic periods. 



ORDER I. URODELA (= Ichthyomorpha, Owen ; Saurobatra- 

 chia]. This order is commonly spoken of collectively as that 

 of the " Tailed " Amphibians, from the fact that the larval tail 

 is always retained in the adult. The Urodela are characterised 

 by having the skin naked, and almost invariably destitute of 

 any exoskeleton. The body is elongated posteriorly to form a 

 compressed or cylindrical tail, which is permanently retained 

 throughout life. The dorsal vertebrae are biconcave (amphi- 

 cczlous], or concave behind and convex in front (ppisthocalous), 

 and they have short ribs attached to the transverse processes. 

 The bones of the fore-arm (radius and ulna) on the one hand, 

 and those of the shank (tibia and fibula] on the other, are 

 not anchylosed to form single bones. 



The best known of the existing Urodela are the Newts 

 (Triton], the Salamanders (Salamandra], the Mud-eels (Siren], 

 the Axolotl (Siredon], and the Giant-Salamanders (Menopomd). 

 Some of these are " perennibranchiate," retaining the bran- 

 chiae throughout life ; others lose the branchiae, becoming thus 

 " caducibranchiate," but retain the branchial apertures behind 

 the head ; others, lastly, lose both the branchiae and the bran- 

 chial apertures. Most of the Urodela have the four limbs 

 well developed, but some possess only the anterior limbs. 



The geological history of the Urodela is short and of little 

 importance. No trace of the order has hitherto been discovered 

 in any deposits older than the Tertiary. The only exception 

 to this statement is constituted by the fossil described from the 

 Lower Permian Rocks by Geinitz under the name of Palceo- 

 siren, and regarded by him as being m^st nearly allied to the 

 Siren lacertina. It is probable, however, that Palczosiren is 

 really referable to the Labyrinthodontia. In strata of Tertiary 

 age have been discovered the remains of Newts and Sala- 

 manders. The most remarkable fossil referable to this order 

 is the Andrias Scheuchzeri (fig. 307) of the Miocene beds of 



