72 MR. E. R. ALSTON ON THE ORDER GL.1RES. [Jan. 18, 



nostrils pointed above, sigmoid or linear. The ears are very generally 

 einarginate behind ; and the tail, when present, is cylindrical, hairy, 

 «caly, or subnaked. 



In the division of the hystricine Rodents intofamihes much diver- 

 sity of opinion has prevailed. Mr. Waterhouse, laying too great 

 stress on dental characters, entirely separated the Dasyproctina from 

 the Caviina, and placed them between the/7r/s^n'ema proj)er and the 

 Echimyina*. Prof. Brandt reunited the two former in his family 

 Hemionychoides, equivalent to the Subungulata oi Illigert. But the 

 group thus formed is so ill defined that Prof. Lilljeborg found it im- 

 possible to separate it from the Hystricidcet- It seems to me that, 

 although Mr. Waterhouse was certainly misled in entirely separating 

 the Agoutis and Pacas from the Cavies and Capybara, they must still 

 be ranked as distinct but allied families, and that the same value 

 must be given to the curious form named Dinomys by Dr. Peters§. 

 Accordingly I would recognize six families of the Hystricoynorpha. 



Of these the first, the Octodontid(S, consists of three subfamihes ; 

 for here, I think, must be placed the Ctenodactyli7iw, formerly asso- 

 ciated with the Jerboas, but of wliich the hystricine affinities have 

 been established by Dr. Peters |1. The other subfamilies are the Octo- 

 dontiiKB and Echi'nomyinte of Mr. Waterhouse. Some of the genera 

 of the latter make a close approach to the next family, the Hystri- 

 cidcc, which in its turn is composed of two very distinct subfamilies, 

 Sphingurina and Ilystricina; ; for I cannot follow Professor Lillje- 

 borg in relegating the former to the Octodontida% principally on 

 account of their better-developed clavicles, which are probably an 

 adaptive peculiarity connected with their arboreal habits. Of the 

 remaining familiesthe ChinchilJidcB form a small but very natural 

 o-roup, connected in some cliaracters with the l)inomyid(e ; and the 

 Tatter, again, has close afiinities with the nearly allied Dtisijproctidce 

 and Caviida. These latter families in many points, as in the mode 

 in which their incisors wear down, their emarginated palates, and 

 the large size of their basicranial foramina, show a striking ap- 

 ))roach to the next great group of Rodents. 



The second suborder, Glires duplicidentati, containing only 

 two families, is clearly less speciahzed than the first, and appears to be 

 a survivor, representing a comparatively early stage in the develop- 

 ment of the Rodent type. At birth, the upper jaw contains the 

 normal number of incisors; but oidy the two inner pairs are retained ; 

 and of these the second remain very small, and are placed directly be- 

 hind the large middle pair. In the mandible there is never more than 

 one pair. Another important proof of the inferior degree of speciali- 

 zation in the Glires dvpUcidentati is the fact that the enamel of the 

 incisors may be traced round to their posterior surface, though it is 

 here much thinner than in front**. Of cranial characters, it may be 



* Nat. Hist. Mamm. ii. p. 360. t Prod. Syst. Mamm. p. 92. 



+ Op. cif. p. 54. 



^ Festschrift. Gesellscli. nat. Freunde, pp. 227-234 (1873). 



il Tr. Z.,S. vii. pp. 397-409. H Oj). cif. p. 51 , 



*^ Cf. Oweu, Conip. Anat. Yort. iii. p. 296. 



