ii8 NATURAL SCIENCE. Feb., 



intermediate form which must apparently be recognised as a third 

 species. 



Having two imperfectly-known named species of a genus from a 

 particular formation, one would naturally have thought that the 

 object of the palaeontologist would be to endeavour to complete our 

 knowledge of those two species, and to hesitate to name new species 

 (not to mention genera) from remains of the same group of animals 

 from the beds in question, without the clearest possible evidence of 

 their right to distinction. Such a method of procedure seems, 

 however, to be utterly at variance with the views of certain South 

 American so-called palaeontologists, to whom the task of describing 

 the fossil mammals in the La Plata Museum has been unfortunately 

 from time to time confided. Instead of endeavouring to find out 

 whether the specimens before them might not belong to one or the 

 other of the two named species of Nesodon, they appear to have 

 started on the assumption that almost every single bone or tooth that 

 came under their notice must pertain to a totally new animal. In 

 consequence, we have remains which clearly belong either to one or 

 other of the two Owenian species, or to the above-mentioned inter- 

 mediate form, assigned to something like a dozen genera (such as 

 Acrothevkim, Adinotherium, Atvypothevmm, Colpodon, Nesotheriujii, Grono- 

 thevium, Phobereotheriuni, Protoxodon, and Scopothermm) ; while the 

 number of nominal species must, I should think, be fully half-a- 

 hundred. As a result of this extraordinary method of procedure, an 

 enormous proportion of the specimens in the La Plata Museum are 

 "types," whereby that institution is prevented from doing as much 

 in the way of exchange as would otherwise be practicable. This 

 remarkable ignorance of the first principles of odontological anatomy, 

 and of the different forms assumed by teeth according to the ages of 

 their owners, displayed by the palaeontologists in question, surpasses 

 belief, and there are certain specimens in the Museum bearing 

 different generic names which even any ordinary student would say 

 were identical. Indeed, on the principle (or, rather, want of principle) 

 which appears to have guided the Argentine palaeontologists, about a 

 dozen species and some half-a-dozen genera might easily be made 

 out of remains of the common horse. It is true that Nesodon displays 

 an extraordinary degree of variation in the relative proportions of the 

 large incisors in both jaws, but the gradual evolution of the adult 

 from the young stage is indicated over and over again in the collection 

 of the Museum ; and with regard to the species founded on the 

 evidence of the cheek-teeth, there is not the least excuse. This, 

 however, is not all, for some of the so-called genera have actually 

 been assigned to families apart from Nesodon ; while the latter itself 

 is separated, as a family, from the Toxodontidae without the faintest 

 shadow of justification. 



I must, however, do one of the above-mentioned workers the 

 justice of saying that he has at last partially seen the errors of his 



