PEKMIAtf FAUNA. 155 



type of organisation in the rudimentary or embryonic condition of 

 the vertebral column, which is in most cases only partially ossified. 



The Amphibia of the Permian period are by most authors placed 

 in the single group of the Labyrinthodontia, although in certain 

 structural departures from the normal type, as in the very rudi- 

 mentary condition of the vertebral column, and in the absence of 

 the peculiar labyrinthine infolding of the enamel of the teeth, some 

 of the forms may have to be separated from this order. Most of 

 the species were provided with a tail of greater or less length, and 

 the general resemblance to living amphibians appears to have been 

 mainly with the salamandoids, although in several points of struc- 

 ture they more closely approximate the tailless frogs and toads. 

 The relationship with the plated ganoids is well pronounced, and 

 not improbably some of these, as dipneusts, or double breathers, 

 may have been their true ancestors (as well as of the lung-fishes 

 proper, Dipnoi). Among the more prominent genera are Branchio- 

 saurus, Melanerpeton, Urocordylus, Archegosaurus, Eryops, Palaeo- 

 siren, and Ophiderpeton, the last two apparently apodal, and re- 

 calling the co3cilians in outline. In Eryops megacephalus, the 

 largest of American amphibians, from, the Permian of Texas, the 

 skull measures eighteen inches in length and twelve inches in 

 breadth. 



The fish-fauna of this period partakes essentially of the char- 

 acter of the fauna of the period preceding, from which it has 

 borrowed most of its types. We have here, however, the first 

 unequivocal remains of the genus Ceratodus (Bohemia and Texas), 

 which represents the most ancient generic type of all existing 

 Vertebrata. 



Regarding the invertebrate fauna of the period, it may be re- 

 marked that a deficiency in the number of forms is noticeable in 

 nearly all the localities where the Permian deposits are developed, 

 a circumstance due to the peculiar physical conditions under which 

 the deposits were formed, and the subsequent alteration, resulting 

 in the obliteration of the contained organic remains, to which, in 

 many places, the rock-masses were subjected. A very large pro- 

 portion of the known fossils are, as has already been intimated, 

 of clearly Carboniferous types, more especially in the case of the 

 Mollusca. The trilobites, so characteristic of the earlier deposits 

 of the Paleozoic era, are wholly wanting, not a single individual, 



