550 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



In i est tins many (aboul eleven) times as long as the body. Ccccum very large 



( as long as the body). Out Ids of genito-urinary and digestive organs distinct 

 from each other (compare Castoridse). Testes abdominal. Os penis very 



large, cleft at the end. Urethral glands few and simple (no other perineal 

 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 

 1o full family rank, if not to still higher appreciation. Like the equally pecul- 

 iar Castoridce, 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 Sciuridce itself. Thus, in 1858, Professor 

 Baird made Castor and " Aplodontia" together a subfamily Castorince of the 

 family Sciuridce,]- 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 

 18G4, Ilerr W. Peters discussed the genus, comparing the skull with that of 

 Arctomys, and noting the strong resemblance observable in many respects ; 

 Ik 1 is considered by Mr. Alston J to have "definitely established" the Sciurine 

 affinities of the genus. In 1866', Professor Lilljeborg (I. s. c.) first, as far as 

 I can ascertain, cleared the way for the required improvement in classification, 

 by raising the ^cniis to the rank of a family, which he called Haphodonlid >, 

 and placed next after Sciurida? ; although, as Mr. Alston (/. i. c.) observes, he 



* For example, in 1840, Scbinz threw "Aplodontia" into his VII " family " of Glires, " Canieularia " 

 which consisted of an odd jumble of Haplodon, "Aseomys" (=Geomyg), Thamomys, Siphneiis, Ctenomys 

 Spalax, and various otbei harrowing Rodents ; as bucu, being beneath serious criticism. 



tBaird's family Sciuridce, however, inclnded the Murine family Myoxida; treated as a snbfamiry 

 Myoiitiw. 



! P. Z. S. 1876, GO. 



