386 PERSISTENT TYPES OF LIFE 



ancient animal world is greater, but still singularly small. 

 No fossil animal is so distinct from those now living as to 

 require to be arranged even in a separate class from those 

 which contain existing forms. It is only when we come 

 to the orders, which may be roughly estimated at about 

 a hundred and thirty, that we meet with fossil animals 

 so distinct from those now living as to require orders 

 for themselves ; and these do not amount, on the most 

 liberal estimate, to more than about 10 per cent, of the 

 whole. 



There is no certainly known extinct order of Protozoa ; 

 there is but one among the Ccelenterata that of the 

 rugose corals ; there is none among the Mollusca ; there 

 are three, the Cystidea, Blastoidea, and Edrioasterida, 

 among the Echinoderms ; and two, the Trilobita and 

 Eurypterida, among the Crustacea ; making altogether 

 five for the great sub - kingdom of Annulosa. Among 

 Vertebrates there is no ordinaily distinct fossil fish : there is 

 only one extinct order of Amphibia the Labyrinthodonts ; 

 but there are at least four distinct orders of Reptilia, viz. 

 the Ichthyosauria, Plesiosauria, Pterosauria, Dinosauria, 

 and perhaps another or two. There is no known extinct 

 order of Birds, and no certainly known extinct order of 

 Mammals, the ordinal distinctness 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 ordinally 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 Paleozoic age. Lastly, 

 the Reptilia present the extraordinary and exceptional 

 phenomenon 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 paleontological evidence tending 

 towards the same conclusion afforded by the existence of 

 what he termed " persistent types " of vegetable and of 



