PALEONTOLOGY. 35 



Brontotheridrc. He has also described a number of 

 small, but very interesting Jurassic mammalia, closely 

 related to those found in our Stonesfield Slate and 

 Purbeck beds, for which he has proposed a new order, 

 1 Prototheria.' Lastly, I may mention the curiously 

 anomalous Reptilia from South Africa, which have been 

 made known to us by Professor Owen. 



Another important result of recent pakeontological 

 research is the law of brain-growth. It is not only in 

 the higher mammalia that we find forms with brains 

 much larger than any existing, say, in Miocene times. 

 The rule is almost general that as Marsh has briefly 

 stated it ' all tertiary mammals had small brains.' 

 We may even carry the generalisation further. The 

 cretaceous birds had brains one- third smaller than those 

 of our own day, and the brain -cavities of the Dinosauria 

 of the Jurassic period are much smaller than in any 

 existing reptiles. 



As giving, in a few words, an idea of the rapid pro- 

 gress in this department, I may mention that Morris's 

 1 Catalogue of British Fossils,' published in 1843, con- 

 tained 5,300 species ; while that now in preparation by 

 Mr. Etheridge enumerates 15,000. 



But if these figures show how rapid our recent pro- 

 gress has been, they also very forcibly illustrate the 

 imperfection of the geological record, giving us, I will 

 not say a measure, but an idea, of the imperfection of 

 the geological record. The number of all the described 

 recent species is over 300,000, but certainly not half 

 are yet on our lists, and we may safely take the total 

 number of recent species as being not less than 700,000. 

 But in former times there have been at the very least 



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