66 PEOCEEDIXGS OF THE GEOLOGICAL SOCIETY. 



remarkable manner, as no one would be more ready to admit than 

 the author of it himself. 



There is no little difficulty in making a calculation of the pro- 

 portion of living to extinct orders, owing to the discrepancies in 

 the opinions of zoologists and comparative anatomists as to what 

 are the characters which ought to be regarded as of ordinal value. 

 For my present jmrpose I very gladly avail myself of the useful 

 Synopsis of the Animal Kingdom prepared by Mr. E. T. Xewton, 

 which is " founded on the Classification proposed by Professor 

 Huxley, with such modifications as are rendered necessary by recent 

 discoveries." 



We may, I think, take the whole number of living orders of 

 animals generally accepted by zoologists at about 108. But in 

 any comparison of these with fossil forms it is only fair to ex- 

 clude from our consideration such as possess no hard parts and 

 stand little or no chance of being preserved in a fossil state. Few 

 would be bold enough to doubt that such soft-bodied forms must 

 have existed in the past, or that they probably bore about the same 

 proportion to the forms with hard skeletons as in the existing fauna ; 

 even the boldest sceptic on this subject would, I should think, be 

 convinced by such singular accidents as that of the finding of the 

 impressions of Rliizostomites, one of the Discophora, preserved in 

 the soft calcareous mud of the Solenhofen Slate. 



Xow among the 108 living orders of animals, at least 36 are 

 totally destitute of any hard parts capable of being preserved in a 

 fossil state, and we have thus left 72 living orders with which our 

 comparison of the extinct ones must be made. 



What is the number of orders which must be created to receive 

 extinct forms, is a question that has given rise to wide diversities 

 of opinion in recent years. While few naturalists would consider 

 18 as an excessive estimate, there are others who would probably 

 double that number. 



Taking the lower estimate and comparing the 18 extinct orders 

 with the 72 living ones which contain animals with hard parts, we 

 find the proportion of extinct orders to be 20 per cent, of the whole 

 number known at the present time. 



But, in comparisons of this kind, it must be remembered that 

 there is an unconscious tendency among the students of recent 

 forms of life to underestimate the differences between extinct and 

 living forms. If we take such groups as the Grapzolitidce, the 

 Monticidi^oridce, and the JStromatojporidce, of the nature of the 



