"18 INDEX GENERUM MAMMALIUM. 
respects to adopt a system of classification which would reflect mod- 
ern views and at the same time meet the needs of the index. If 
too conservative an arrangement of the higher groups were adopted 
the families would often be so broad that the lists would be long and 
unwieldy, and include names of genera which are now recognized as 
belonging to distinct groups. If, on the other hand, too much subdi-. 
vision were attempted the names of related genera would be scattered 
under several families which, on account of the alphabetical arrange- 
ment, would not be in close proximity. The following arrangement 
is therefore more or less of a compromise, and is not to be regarded 
in any sense as an ideal system of classification, but merely as a 
system adopted especially to meet the needs of the present work 
and to facilitate comparison of the generic names. It can hardly be 
expected that this arrangement will meet with general acceptance, 
especialiy in the case of some of the extinct groups; but when genera 
are subject to such frequent and violent changes as are common in 
paleontology—when, for example; a group is shifted from the Pri- 
mates to the Glires, as in the case of JMzrodectes"—1it is almost impos- 
sible to find a scheme of classification which will be stable for any 
length of time. 
The treatment of families is conservative, but at thesame time most 
of the groups which are currently recognized —nearly two hundred in 
number—have been admitted. 
The classification adopted follows, in the main, that of Flower and 
Lydekker's * Mammals, Living and Extinct’ (1891), but with modifi- 
cations in many cases. Thus the Edentata have been divided into two 
orders, the Edentata and Effodientia; the Creodonta and- Tillodontia 
are recognized as full orders, and the Astrapotheroidea and Typo- 
theria given subordinal rank under the Ungulata.’ In extinct groups, 
Hay's * Bibliography and Catalogue of Fossil Vertebrata of North 
America? (1902), Trouessart’s * Catalogus Mammalium' (1897-99), and 
Zitte’s ‘Handbuch der Paleontologie" (1892-93) have been the 
guides. In the Cete, Beddard, Gray, and True have been consulted, 
and in the Chiroptera and Insectivora, Dobson's classification has been 
followed in the main. The arrangement of the extinct Edentates is 
largely that of Zittel, with modifications from recent papers of 
Ameghino. The classification of the Glires is that outlined by Thomas 

«See OssonN, Bull. Am. Mus. Nat. Hist., XVI, 203, 206, 1902. 
» According to some authors the groups of Ungulata usually treated as suborders 
are entitled to ordinal rank. Thus Scorr ( * Introduction to Geology,’ p. 548, 1897) 
does not recognize the Ungulata, but gives the Amblypoda, Artiodactyla, Condy- 
larthra, Litopterna, Perissodactyla, Proboscidea, Toxodontia, and Typotheria as full 
orders. It is more convenient, however, for present purposes to consider these 
groups as divisions of the Ungulata and keep them together, instead of having them 
scattered, as would be the case under the alphabetical arrangement. 
