552 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
of the Sciurine series. Briefly, then, I at present accept a superfamily group 
Sciuromorpha in the sense lately attached to it by Mr. Alston, as including 
the genus Sciwrus and its unquestioned allies, as wellas Haplodon, Castor, and 
Anomalurus, with which latter I am acquainted only by descriptions. Since 
Waterhouse, many years ago, foreshadowed a more refined classification of 
the Rodents by his four families of Scturide, Muride, Hystricidz, and 
Leporide, there has been a close general agreement among leading writers 
that these groups, whatever their absolute rank, represent as many natural major 
divisions of existing Rodents. The Leporide, by nearly common consent, are 
now cousidered as one of two primary divisions of recent Gdires, as such 
comparable in value to all the families of “simplicidentate” Rodents com- 
bined. The Scturide, Muride, and Hystricide of Waterhouse, with whatever 
modification in details, yet stand as indices of groups of Rodents, of whatever 
value we may assign, the members of each of which are much more nearly 
interrelated than any one of them is to any member of either of the other 
eroups. In the paper already several times cited, Mr. Alston seems to me to 
have defined the three groups, which he calls simply “‘sections”, in a very 
satisfactory manner; and he certainly has given us an easy means of distin- 
guishing them. ‘Even if it were not possible to separate the first three of 
Waterhouse’s great families by perfectly constant characters,” says Mr. Alston, 
“they ought, as it appears to me, to be recognized as indicating three distinct 
lines of development. But by the help of the characters of the leg-bones, 
pointed out by Professor Lilljeborg, the difficulty is overcome. In the few 
cases in which the cranial differences fail us in separating the Sciurine rodents 
from the Murine, and the latter from the Hystricine, the complete anchylosis 
of the lower part of the tibia and fibula in the second group comes to our 
ad. . . . . The first and third groups, which agree with one another in this 
point [distinction of fibula], are at once separated from each other by the form 
of the mandible, a8 well as by the whole type of cranial structure. . . . . 
The first section, Sciwromorpha, has for constant characters the combination 
of a peculiar form of mandible with the persistence of the fibula as a distinet 
bone throughout life. The former character at once separates it from the 
-Hystricomorpha, the latter from the Myomorpha.” This is the sense, then, 
in which Tam to be understood to accept the Sciwromorpha, in my present 
reference of the Haplodontide to that series as one of its component families, 
