F. AmecjMno — Geology of Argentina. 7 



fairness on the part of the author in not having mentioned that the 

 first notices of the remains of these animals and the determination 

 that they belonged to Dinosaurs, were made by me in various 

 publications, some prior to the foundation of the Museum at La 

 Plata ;^ and the greater part of the remains of Titanosam-us figured 

 by the author formed part of my old collection,'^ I not having 

 described them for reasons which need not be mentioned. 



However that may be, the presence of the Dinosauria in the 

 formation of red sandstones is of the highest importance, not only 

 from the palfeontological point of view, but also because they form 

 a fixed point of departure for the determination of the geological 

 age of the strata resting upon them. These animals are essentially 

 characteristic of Mesozoic times, and with their disappearance in 

 Europe and North America coincides the appearance of the placental 

 mammals, especially of the ungulates. In Patagonia the beds with 

 remains of Dinosaurs pass insensibly into other beds with numerous 

 remains of mammals, particularly of ungulates, which circumstance 

 proves that the red sandstones ought to be referred to the Upper 

 Cretaceous. 



The Pyrotherium Formation. 



This brings us to the somewhat more modern deposits, which 

 I have designated with the name of Pyrotherium Formation 

 (" Couches a Pyrotherium," in Bol. Inst. Geogr. Argent., vol. xv, 

 pp. 603-8), specially intending not to prejudge their geological 

 age ; but, according to my first impression, which has not hitherto 

 been in any way modified, they ought to be assigned to the most 

 modern series of the Cretaceous formation. 



The mammal-fauna of the Pyrotherium beds is one of the greatest 

 interest, and its discovery is destined to elucidate many biological 

 mysteries concerning the origin of the different groups of the class 

 Mammalia. 



In 1895 I gave a description of the principal types at that time 

 known,^ but the later explorations of Carlos Ameghino have 



1 F. Ameghino, Bol. Acad. Nac. de Cienc, vol. viii, 1885, p. 150 ; and " Contrib. 

 conoc. maniif. fos. Repub. Argent.," 1889, pp. 16, 899, 959. The first remains of 

 Dinosaurs met with in Patagonia, consisting of a complete caudal vertebra and 

 a large rib with the articular head complete, were found in the JSTeuquen in the year 

 1882 by Captain Buratowich, and presented by him to the then President of the 

 Republic (General Juho A. Eoca), who in his turn presented them to me, and 

 I immediately determined them as belonging to a gigantic Dinosaurian (see la Nacion, 

 March 23, 1883). This was the first notice of the former existence of these singular 

 extinct reptiles on the soil,of the Argentine Eepublic. 



- These remains, from Fort Roca, were presented to me by their discoverer, Senor 

 Don Jorge Rohde, then Captain (now Colonel) of the Military Engineers. 



3 F. Ameghino, "Premiere Contribution a la Counaissance.de la Faune Mamma- 

 logique des Couches a Fy r other ium '^ : Bol. Inst. Geogr. Argent., vol. xv, 1895, 

 pp. 603 61. In reference to this work, Mr. S. P. Palmer, of the U. S. Department 

 of Agriculture, who is editing a " Nomenclator " of the known genera of mammalia, 

 writes to me that the names Clorinda and Etirygenium, with which I have designated 

 two extinct mammals from this formation, have been previously employed for other 

 animals. The observation is correct, and it is all the more strange since I had not 

 noticed that the two generic names are recorded in Scudder's " Nomeuclator 

 Zoologicus," which I always have at hand. I am thus compelled to change those 

 names, replacing that of Clorinda by Flagiarthrus, and that of Eurygenium by 

 Eurygeniops. 



