550 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
Intestines many (about eleven) times as long as the body. Cacum very large 
(as long as the body). Outlets of genito-urinary and digestive organs distinct 
from each other (compare Castoride). Testes abdominal. Os penis very 
large, cleft at the end. Urethral glands few and simple (no other perinzal 
glands ?). 
For other characters, derived from the external structure, and properly 
to be considered as rather pertaining to the genus than to the family, see 
under next head. 
As may be gathered from the foregoing epitome of the more salient 
anatomical characters, the present is a remarkably peculiar group, entitled 
to full family rank, if not to still higher appreciation. Like the equally pecul- 
iar Castorida, it has, as one author has remarked, long proved a stumbling- 
block in the way of a systematic arrangement of the Rodents; but for no 
other reason, as it seems to me, than because authors long regarded the type 
of structure as only significant of a genus, a place for which was to be 
found perforce among the then established families, instead of recognizing its 
claims to higher valuation. It would be idle to recount the various forced 
associations to which the family considered as a genus has been subjected.* 
The general tendency has been, however, of late years at any rate, to associ- 
ate Haplodon more or less intimately with Castor, and to refer both genera to 
the Sciurine series, if not to the Sciwrid@ itself. Thus, in 1858, Professor 
Baird made Castor and ‘Aplodontia” together a subfamily Castorine of the 
family Sceurcde,t inquiring pertinently whether the two were not typical of 
as many distinct subfamilies, themselves forming a group of full family rank. 
Professor Brandt, had already, in 1855, placed the genus next to Castor. In 
1864, Herr W. Peters discussed the genus, comparing the skull with that of 
Arctomys, and noting the strong resemblance observable in many respects ; 
he is considered by Mr. Alston ¢ to have ‘definitely established” the Sciurine 
affinities of the genus. In 1866, Professor Lilljeborg (Z. s. c.) first, as far as 
I can ascertain, cleared the way for the required improvement in classification, 
by raising the genus to the rank of a family, which he called Haploodontidz, 
and placed next after Sciwride ; although, as Mr. Alston (2 7. c.) observes, he 
* Por example, in 1840, Schinz threw “Aplodontia” into his VII “ family ” of Glires, “ Cunicularia” 
which consisted of an odd jumble of Haplodon, “Ascomys” (= Geomys), Thomomys, Siphneus, Clenomys, 
Spalar, and yarious other burrowing Rodents; as such, being beneath serious criticism. 
t Baird’s family Seiuridw, however, included the Murine family Myoxide, treated as a subfamiky 
Myoxina. 
} P. Z. 8. 1876, 66. 
