aves. 323 



tertiary period,- and to have begun to decline after that time ; 

 whilst the tailless genera and species are most numerous 

 and various at the present day. The Ophidia resemble the 

 Anoura, commencing in the older tertiary, and shewing 

 their maximum of development at the present day. The true 

 proccelian, and especially the pleurodont, lizards, commencing 

 in the chalk, have also gone on increasing in number and 

 variety of forms to the present day. The acrodont group was 

 represented by Mosasaurus, with a maximum of size, and 

 extreme modifications for marine life, during the cretaceous 

 period. The great ordinal groups of Ichthyo- and Sauro- 

 pterygia, of Pterosauria, and Dmosmtria, together with the 

 amphi- and opistho-coelian Crocodilia, passed away ere the 

 tertiary time had dawned. The proccelian crocodiles, which 

 culminated in the lower and middle tertiary times, are now 

 on the wane. Perhaps, also, the same might be said of the 

 Chelonia, in regard to the size of individuals and the number 

 of species of certain genera (e.g., Chelone, Trionyx, Chelydra). 



Class III.— AYES. 



Long before any evidence of birds from actual or recog- 

 nizable fossil remains is obtained in tracing the progress of 

 life from the oldest fossiliferous deposits upwards, we meet 

 with indications of their existence impressed in sandstones of 

 the triassic or liassic period. 



These earliest evidences of the class are by footprints in 

 some former tidal shore, preserved in one or other of the ways 

 explained in the section "Ichnology." The fossil bones of 

 birds have hot been found save hi strata of much later date 

 than the impressed sandstones ; and they are much more rare 

 than the remains of mammals, reptiles, and fishes, in any 

 formations except the most recent in certain limited localities, 

 — e.g., New Zealand. 



