F. Ameghino — Geology of Argentina. 13 



impossible to attribute them to an age more recent than the Upper 

 Cretaceous. 



From my point of view there has hitherto been advanced only 

 a single sufficiently serious argument against the antiquity of the 

 Patagonian Formation, and it consists in the presence of numerous 

 remains of Cetacea, which (if we except the Zeuglodonts, which are 

 undoubtedly very different animals) only appear in Europe and 

 North America during the Miocene period. But we are dealing 

 with a negative proof, the worth of which is only apparent, since 

 it does not take into account the fact that these animals appear there 

 completely developed, without their predecessors being known, and 

 certainly they did not fall from the sky, but went there as emigrants 

 from other regions. The Cetacea, indeed, are a group of mammals 

 which arose in South America and emigrated to the northern 

 hemisphere, at a comparatively recent geological period, when they 

 had already acquired all their principal distinctive characters. 



It is enough to glance at the remarkable memoir of Lydekker on 

 the skulls of fossil Cetacea from Chubut^ — Physodon Patagouicus, 

 Lyd., Diaphorocetus Poucheti (Mor.), Amegh.,^ Prosqualodon aus- 

 tralis, Lyd., Argyrocetus Patagonicus, and Diochoticus Benedeni (Mor.), 

 Amegh.^ — which come from Puerto Madryn, from the most modern 

 beds of the Patagonian Formation,* to perceive that we are dealing 

 with more primitive and less specialized types than those obtained 

 from the Miocene deposits of Europe and North America ; this is 

 especially very evident in the genera ArgyrodelpMs and Prosqualodon. 



^ E. Lydekker, " Cetacean Skulls from Patagonia" :< Anal. Mus. La Plata — Pal. 

 Argent., vol. ii, 1894, pt. 2. As I have observed on another occasion, this volume, 

 although it hears the date 1893, appeared more recently, in the month of April, 

 1894. 



^ In his work Lydekker designates this Cetacean with two distinct generic names ; 

 in the heading of the description he employs the name of Hypocetus, which is also 

 met with below the figure on the corresponding plate, while at the end of the 

 description he uses the name of Paracetus in substitution for that of Ifesocetus, which 

 Moreno had given to replace this latter, preoccupied for another genus of the same 

 group. For my part, I had already replaced the name of Mesocetns by that of 

 Diaphorooetus (F. Ameghino, Bol. Acad. Nac. Cienc, vol. xiii, p. 437), placing the 

 genus, though only in a provisional way, among the Pontoplanodidse, since my 

 principal object was to give a complete list of all the Tertiary mammals of Pata- 

 gonia. I ought to observe that in reality the genus in question exhibits no relation- 

 ship with the latter group, but with that of the Physeteridaj, as observed by Lydekker, 

 who, notwithstanding this, places it with Physodon in a new family, which he terms 

 PhysodontidiB. In accordance with the opinions expressed by Cope, it does not 

 appear to me that the presence of teeth in the upper jaw is a character sufficient to 

 justify the creation of a new family, since they are also found, though in less number, 

 in representatives of some species of the allied existing genera (E. D. Cope, " Fourth 

 Contribution to the Marine Fauna of the Miocene Period of the United States ' ' : 

 Proc. Amer. Phil. Soc, vol. xxxiv, 1895, p. 135). 



^ Lydekker proposes for this genus the name of Aryyrodelphis to replace that of 

 Notocetus, imder which Moreno had described it, because this, latter was already 

 employed by me for another Cetacean. For the same reason I had proposed that of 

 Diochoticus, placing the genus among the Platanistidse, the same arrangement as 

 given by Lydekker (F. Ameghino, Bol. Acad. Nac. Cienc, vol. xiii, p. 438). 



* It appears that neither the exact locality nor the precise geological horizon is 

 known whence was obtained the skull described by Lydekker in the same work under 

 the name of Cetotherium Moreni. 



