ADDRESS. 19 



mainly by Marsh, Leidy, and Cope. Marsh has made known to us the 

 Titanosaurus, of the American (Colorado) Jurassic beds, which is, 

 perhaps, the largest land animal yet known, being a hundred feet in 

 length, and at least thirty in height, though it seems possible that even 

 these vast dimensions were exceeded by those of the Atlantosaurus. Nor 

 must I omit the Hesperornis, described by Marsh in 1872, as a carnivorous, 

 swimming ostrich, provided with teeth, which he regards as a character 

 inherited from reptilian ancestors ; the Ichthyornis, stranger still, with 

 biconcave vertebraj, like those of fishes, and teeth set in sockets ; while 

 in the Eocene deposits of the Rocky Mountains the same indefatigable 

 palaeontologist, among other very interesting remains, has discovered 

 three new groups of remarkable mammals, the Dinocerata, Tillodontia, 

 and Brontotheridaj. 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, * 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 pateontological 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 progress in this de- 

 partment, I may mention that Morris's ' Catalogue of British Fossils,' 

 published in 1843, contained 5,300 species; while that now in pre- 

 paration by Mr. Etheridge enumerates 15,000. 



But if these figures show how rapid our recent progress 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 im- 

 perfection 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 thei'e have been at the very least 

 twelve periods, in each of which by far the greater number of species 

 were distinct. True, the number of species was probably not so large in 

 the earlier periods as at present ; but if we make a liberal allowance for 

 this, we shall have a total of more than 2,000,000 species, of which about 

 25,000 only are as yet upon record ; and many of these are only represented 

 by a few, some only by a single specimen, or even only by a fragment. 



The progress of palaeontology may also be marked by the extent to 

 which the existence of groups has been, if I may so say, carried back in 

 time. Thus I believe that in 1830 the earliest known quadrupeds were 



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