x.] PERSISTENT TYPES OF LIFE. 217 



Vertebrates there is no ordinally distinct fossil fish : 

 there is only one extinct order of Amphibia — the Laby- 

 rinthodonts ; but there are at least four distinct orders 

 of Eeptilia, viz. the Ichthyosauria, Plesiosauria, Ptero- 

 sauria, Dinosauria, and perhaps another or two. There 

 is no known extinct order of Birds, and no certainly 

 known extinct order of Mammals, the ordinal distinct- 

 ness of the " Toxodontia " being doubtful. 



The objection that broad statements of this kind, after 

 all, rest largely on negative evidence is obvious, but it 

 has less force than may at first be supposed ; for, as 

 might be expected from the circumstances of the case, 

 we possess more abundant positive evidence regarding 

 Fishes and marine Mollusks than respecting any other 

 forms of animal life ; and yet these offer us, through the 

 whole range of geological time, no species ordinarily 

 distinct from those now living; while the far less 

 numerous class of Echinoderms presents three, and the 

 Crustacea two, such orders, though none of these come 

 down later than the Palaeozoic age. Lastly, the Eeptilia 

 present the extraordinary and exceptional pheenomenon 

 of as many extinct as existing orders, if not more ; the 

 four mentioned maintaining their existence from the 

 Lias to the Chalk inclusive. 



Some years ago one of your Secretaries pointed out 

 another kind of positive palaeontological evidence tend- 

 ing towards the same conclusion — afforded by the 

 existence of what he termed " persistent types " of vege- 

 table and of animal life. 1 He stated, on the authority 

 of Dr. Hooker, that there are Carboniferous plants which 

 appear to be generically identical with some now living ; 

 that the cone of the Oolitic Araacaria is hardly distin- 



1 See the abstract of a Lecture " On the Persistent Types of Animal Life, 

 in the "Notices of the Meetings of the Royal Institution of Great Britain/ 

 — June 3, 1859, vol. iii. p. 151. 



