324 Lydehlier''s Contrihuiions to the Palceontologia Argentina. 



Museum, and does not attempt to give a complete synonymy of 

 those which he recognises as valid. 



The suborder Toxodontia is first discussed, and its members are 

 regarded as phylogenetically " related to the Perissodactyla, but as 

 retaining certain features now common to the Artiodactyla, which have 

 probably been inherited from common Condylarthrous ancestors." 

 The suborder is subdivided into three families — the Pachyrucidse, 

 Typotheridee, and Toxodontidee. Of these the first includes two 

 genera, Fachyrucus and Hegetotlieriiim, the species of which are all 

 of small size, and are characterized by the absence of internal 

 enamel folds in the upper molars, by the antero-posterior elongation 

 of the mandibular condyle, and, in Fachyrucus at least, by the 

 jiossession of perfectly unguiculate feet. The author lays some 

 stress upon the rodent-like appearance of these forms, which, how- 

 ever, he regards merely as the result of convergence. In the 

 Typotherida3 is included the genus Typotherium only. The family 

 Toxodontidge embraces the genera Toxodon, Toxodonfotherhim, Xoto- 

 don, Stenostephanus, and Nesodon. Under most of these there is a 

 more or less imposing list of synonyms ; but the climax is reached 

 in the case of Nesodon, of which no less than ten synonymous generic 

 terms are given, while of the species Nesodon imbricatus and N. 

 'patagonicus the specific names are said to be countless. Some ex- 

 planation of this unfortunate condition of affairs is to be found in 

 the extraordinary changes, here fully described, which are under- 

 gone by the dentition at different ages in animals of this genus ; but 

 many of the names seem to have been perpetrated without a shadow 

 of excuse. 



A new suborder, the AstrapotJieria, is established for the reception 

 of the families Homalodontotheridse and Astropotheridse, which it 

 was found impossible to include in the Toxodontia, Litopterna, or 

 Perissodactyla. 



In the Litopterna the author places the Proterotheridge (including 

 the genera Diadinphorus, Epitherium, and Proter other ium) and the 

 jMacrauchenidEe (with the genera Oxyodontotherium, Scalabrinia — a 

 name substituted for the barbarous compound Scalabrinitherium — 

 and Macrauchenia). In this latter family the author states that 

 there is a gradual increase in size and specialization from the older 

 Patagonian Tertiaries to the later Pampean deposits. 



In the Perissodactyla three genera of the Equidae, Equus, Eippi- 

 dium, and Onohippidium, are recognised, Burmeister's opinion that 

 Hippaplus is mei'ely founded on worn teeth of Hippidiiim being 

 confirmed. Both Hippidium and Onohippidium are remarkable for 

 the great backward prolongation of the nasal slits; Onohippidium is 

 further notable for possessing enormous lachrymal fossae. 



Bibodon limbatum, a reputed tapir, is now found to be a member 

 of the Sirenia, and is perhaps referable to Ealiiherium or Prorastoma. 

 The Memoir concludes with an account of some of the Artiodactyla. 



The plates, some forty-three in number, with which these 

 Memoirs are illustrated are very beautiful examples of what may be 

 done in this direction by photography, but at the same time the 



