Vlll INTRODUCTION. 



Phocidce and Trichechiclce and the Physeteroid Cetacea, reductions in 

 these respects will be necessary l . There is of course the danger 

 that the principle in question may be carried to an extreme, and it 

 will perhaps prove that in some instances the remains of more than 

 a single species have been included under one name ; this, however, 

 the writer regards as a less serious error than its reverse. 



It may be observed that this work, as its title implies, is merely 

 a Catalogue of the species and genera represented in the Collection 

 of the Museum, and consequently that it does not embrace all the 

 known Fossil Mammalia. I am indeed well aware how valuable 

 a work of the latter nature would be if it could be made reliable 

 and complete ; but when I consider the number of names that 

 have been relegated to the rank of synonyms from the examination 

 of the specimens in the Museum, and the great uncertainty still 

 existing as to the generic and specific determination of an immense 

 number of the forms unrepresented in the Collection, I am convinced 

 that the time has not yet arrived when such a work could be pro- 

 fitably undertaken. This is indeed well illustrated at the present 

 time in the case of the Mammals of the infra-Pampean formation 2 of 

 South America, whose history is now undergoing a phase very like 

 that experienced in the case of those of North America some few 

 years ago. Thus, in the Bulletins of the Academy of Sciences of 

 Cordova, Signor Ameghino proposes a host of new generic and specific 

 names for the Mammals from this formation ; but as these memoirs 

 are without illustrations, it is often totally impossible to form any 

 conclusion as to the validity of these generic and specific terms ; of 

 which Dr. Burmeister, of Buenos Ayres, considers a large proportion 

 are not entitled to stand 3 . 



In respect of classification I have endeavoured throughout not to 

 form any entirely new scheme, and have in the main followed the 



1 If I had been describing the remains of these forms de novo I certainly 

 should not have made the number of genera and species that have been founded ; 

 but as the specimens at present available are not sufficient to say decisively 

 that some of these forms are equivalents of others, the only course has been 

 to refer the specimens to the genera and species to which they appear to belong. 



2 The so-called Eutemnodus mentioned in pt. i. p. 21, note 5, and the Ma- 

 crauchenia in pt. iii. p. 16, are from this formation, and are therefore older than 

 the Pleistocene Pampean. Dr. Burmeister refers the infra-Pampean to the 

 Pliocene, while Signor Ameghino, on the other hand, regards it as representing 

 the European Oligocene. 



3 Another difficulty occurs with regard to existing species, all of which pro- 

 bably date back to the Pleistocene, although only a moiety have been actually 

 recorded as fossils. 



