of 



By J. C. MANSEL-PLEYDELL, Esq., 

 P.L.S., P.G.S. 



HE secondary or Mesozoic age has been rightly 

 designated the age of reptiles ; whole orders 

 rose, grew, and became extinct during its 

 continuance. There were no true reptiles until 

 the Permian, their advent had been previously 

 foreshadowed by a large assemblage of Amphibia 

 during the Palaeozoic age, notably towards its 

 close. This sub-class of vertebratse differ from the mammalia 

 and Reptilia by the embryo having gills which permanently 

 or temporarily perform the respiratory function ; and having two 

 occipital condyles (or protuberances at the end of the bone which 

 attaches the skull to the spinal column) ; also when young, in being 

 provided with branchial arches ; differing from Pisces in their 

 mode of locomotion, their limbs having no fin-rays, assuming the 

 mammalian type as they advance towards maturity. These peculiari- 

 ties were present among Amphibia from their earliest appearance in 

 past geological ages. The Amphibian family comprises four distinct 

 orders, Urodela, Anura, Ophiomorpha, and Labyrinthodontia ; of 

 these Ophiomorpha have not been met with fossilized. All the 

 freshwater deposits from the Trias to the Carboniferous age inclusive, 



