104 
in any previous quarter of a century. New 
methods of collecting, and more thorough ex- 
ploration of regions previously little known, 
have brought to light a host of new forms and 
furnished material for studies which have 
thrown new light on the relationship of many 
groups. More careful examination of the litera- 
ture has likewise necessitated many changes in 
nomenclature. Thus it is not surprising that 
Alston’s classification, which has been generally 
adopted during the last 20 years, should have 
become somewhat antiquated. 
In many respects Mr. Thomas is peculiarly 
fitted for the task of ‘ bringing the arrangement 
of the order up to date.’ As curator of mam- 
mals in the British Museum he has constant ac- 
cess to a collection of rodents, which includes 
representatives of all but 15 of the existing 
genera and is unrivalled in the possession of a 
large number of types. 
zoologist is personally familiar with more species 
or has a better general knowledge of the Ro- 
dentia than Mr. Thomas. He has also done 
much towards placing the nomenclature on a 
sound basis and has kept fully abreast of recent 
morphological work. 
Although his paper comprises only 16 pages, 
it is an unusually important contribution to the 
literature of mammals and its value is not to be 
measured merely by its length. Unlike Alston’s 
paper, it contains no diagnoses, and is therefore 
merely a list of genera arranged by families and 
subfamilies. It is intended mainly as a con. 
venient reference list for museum curators and 
writers who have neither the time nor the in- 
clination to work out the relationships of 
genera. Its object is threefold, since it gives: 
(1) the position and sequence of the genera in 
their respective subfamilies; (2) the earliest 
available name for each genus, and (8) a refer- 
ence to the original description. The results 
of the investigation here presented necessitated 
not only a study of the genera and families, but 
the selection of the proper name from a host of 
synonyms for each of the 160 groups which are 
considered worthy of generic rank. 
It would have been very desirable if the list 
had included extinct as well as living forms and 
had been extended to subgenera, thus forming a 
complete conspectus of the order. In limiting 
SCIENCE. 
Perhaps no other. 
(N.S. Vou. VI. No. 133. 
it to living mammals the author restricted him- 
self to forms with which he is personally famil- 
iar, and by omitting subgenera avoided a vast 
amount of work which would have inevitably 
delayed the appearance of the list. 
The changes which have been made in the 
classification of Rodents during the last 25 
years can be most clearly brought out by com- 
paring the lists of Gill, Alston and Thomas, but 
in so doing it should be remembered that 
Thomas follows Alston as closely as possible in 
the arrangement of the higher groups. Gill in 
1872 recognized 9 superfamilies, 20 families, 16 
subfamilies, but mentioned no genera; Alston 
in 1876 gave 3 superfamilies, 18 families, 23 
subfamilies and 100 genera ; Thomas now ad- 
mits 5 superfamilies, 21 families, 27 subfamilies 
and 161 genera.* The increase in the present 
list is due to elevating the Bathyergidze, Hete- 
romyide, Hrethizontide and Pedetids to the 
rank of families, and reducing the Lophiomyidze 
to a subfamily of Muride. About one half the 
additional genera are ‘new discoveries’ and the 
remainder are due to the breaking-up of old 
genera. 
Recent writers divide the Rodentia into two 
suborders : Simplicidentata and Duplicidentata ; 
and most of them have followed Alston’s tri- 
partite division of the Simplicidentata into 
Sciuromorpha, Myomorpha and Hystricomor- 
pha. This simple arrangement has not proved 
satisfactory, since some of the outlying genera 
will not fit into either group. To meet this diffi- 
culty Thomas has added two groups: Anoma- 
luri and Aplodontiz, making 5 subdivisions of 
superfamily value, thus to some extent follow- 
ing Gill. But in the attempt to retain Alston’s 
higher groups with the termination morpha and 
at the same time to distinguish others of lower 
rank he has introduced two subdivisions be- 
tween family and suborder. The names adopted 
are unfortunate, since the terminations are not 
distinctive, having been used by different au- 
thors for divisions varying in rank from super- 
families to subgenera. It would be simpler to 
*Only 159 are mentioned, but Fiber is inadvertently 
omitted, and Chilomys has been proposed since this 
paper was printed. Beside these Sigmodontomys and 
Zygodontomys have recently been described by Dr. J. 
A. Allen. 
