HAPLODONTIDA—TAXONOMIC CONSIDERATIONS. 551 
“strangely relegated it” to the Hystricine series of Rodents. Dr. T. Gill 
(¢. s. c.) followed Lilljeborg in 1872 in recognizing a family Haploodontide, 
the taxonomic value of which he raised still higher by separating it from 
other Glires as the type and sole member of a ‘‘ superfamily” Haploodontoidea, 
coming next after Castoride, also made the basis of a superfamily Castoroidea. 
Lastly, in 1876, Mr. Alston (/. s. c.) endorsed a family Haplodontide, which 
he placed next to Castoride among Sciuromorpha. 
To waive for the moment the question of absolute rank of the type 
Haplodon, nothing in the way of classifying the Rodents seems to me clearer 
than that the affinities of Haplodon are with Castor, and that both these 
genera appertain to the Sciurine ‘ 
series”, “superfamily”, or “line of develop- 
ment”—at any rate, neither to the Murine nor to the Hystricine series; the 
next nearest relationship of Haplodon being with Arctomys, and so with the 
Sciuride itself. The more or less complete agreement of such views with those 
of the writers mentioned in the foregoing paragraph will be evident without 
further comment; the better informed authors have, in fact, differed less among 
themselves respecting the immediate relationships of Haplodon and Castor than 
in regard to the location of these forms in the general series of simplicidentate 
Rodents ; Haplodon, at any rate, whether considered as genus or as family, 
having been relegated successively to (1) the Sciurine, (2) the Murine, (3) 
the Hystricine series, and (4) having furmed the type of a different series 
from any of these; this, too, at the hands of those who are at one respecting 
its immediate affinities. 
This brings up the question of the absolute standing of Haplodon. Is 
it referable to one of the established series of Rodents, or is it to stand alone 
as the representative of a separate series? Regard for a very strict equiva- 
leney of groups might urge the latter appreciation of the value of the pecul- 
larities of Haplodon; and, in the sense that the family Haplodontide differs 
more from all other families of Rodents than those of the same series usually 
do from each other, Dr. Gill’s special superfamily Haploodontoidea may be jus- 
tified. But, practically, no exact equivalency of groups is attainable; and, if 
it were, I should not be satisfied of the necessity of considering Haplodon to 
represent a separate series from the Sciwromorpha, in view of the closeness of 
relationship which I insist is found between Haplodontide, Castoride, and 
Sciuride. 
In so stating 
g, it becomes necessary to give my appreciation of the limits 
