34 PATAGONIAN EXPEDITIONS : ZOOLOGY. 



of these groups has been assigned, by different authors, the rank of a 

 family, which disposition of them seems fairly to represent their real de- 

 gree of affinity. We would thus have the comprehensive group Octo- 

 dontidae separated into (i) the true Octodonts, or Octodontidae proper; 

 (2) the Spiny Rats and their immediate allies, or Echimyidae ; (3) Cteno- 

 dactylus and allied genera, or Ctenodactylidae. They are severally quite 

 as distinct as are the commonly recognized families Heteromyidas and 

 Geomyidas. 



Genus CTENOMYS Blainville. 



Ctenomys Blainville, Bull. Soc. Philomat, Paris, April, 1826, 64, pi.; 

 Ann. Sci. Nat., IX, 1826, 102. Type, Ctenomys brasiliensis sp. nov., 

 Minas Geraes, Brazil. 



The Tuco-tucos, as the species of Ctenomys are known locally, repre- 

 sent, through closely similar adaptive modifications, in South America the 

 Pocket Gophers (Geomyidae) of North America. Both are modified for 

 an almost exclusive life underground, having the same form of body, fos- 

 sorial feet, degenerate organs of sight and hearing, and the same soft, 

 silky pelage. The Tuco-tucos lack the external cheek-pouches of the 

 Pocket Gophers, and differ from them in certain important cranial charac- 

 ters, although the general form of the skull and the structure of the teeth 

 are similar in both. The form of the zygoma and the position and form 

 of the infraorbital foramen are, however, notably different — features that 

 perhaps warrant their wide dissociation as members respectively of the 

 Hystricomorphs and Myomorphs. 



The Tuco-tucos, as already said, are exceedingly prolific, in local forms 

 as well as in' individuals, and in favorable localities, as in alluvial or moist 

 soils, their burrows fairly honeycomb the earth over considerable areas, 

 rendering traveling, on foot or with horses, more or less difficult and even 

 dangerous. 



Ctenomys magellanicus Bennett. 



Ctenomys magellanicus Bennett, P. Z. S., 1835, 190. Port Gregory, 

 Strait of Magellan; Trans. Zool. Soc. Lond., II, 1841, 84, pi. xvii, 

 animal and skull; same specimen. — Waterhouse, Mamm., II, 1848, 

 283, pi. viii, skull, pi. ix, fig. 2, animal. Based wholly on Bennett's 

 type specimen. — Burmeister, Descrip. phys. Rep. Argent, III, 1879, 

 239, ex Bennett and Waterhouse. — Trouessart, Cat. Mamm., ii, 1897, 



