50 PATAGONIAN EXPEDITIONS I PAL/EONTOLOGY. 



tological characters, their geological age, correlations, physical features, 

 and conditions under which the respective beds were deposited, as far as 

 the material permits any conclusions in these respects. In this general 

 part, several stratigraphical observations of Mr. Hatcher have been antici- 

 pated, which properly belong in the geological part of this work. But 

 since the stratigraphical evidence is absolutely necessary for the correct 

 understanding of the palaeontological facts, Mr. Hatcher has kindly fur- 

 nished all the pertinent data, and permitted their use by the writer. It is 

 hardly necessary to say that the credit for all stratigraphical observations 

 is to be given to Mr. Hatcher, and the writer is satisfied that they are 

 entirely trustworthy, since they agree admirably with the palaeontological 

 facts, and sufficiently explain them. 



In regard to the identification of species, I am greatly indebted to Dr. 

 H. von inenng ^r e~^ rvxuio, bra^i. u- no t only gave his opinion in 

 doubtful cases submitted to him, but sent to tiiv, p r i nce ton Museum a 

 collection of Patagonian as well as Entrerios fossn^ which aided me 

 materially in the correct identification of our material. i t j s on j v p rO p er 

 to express also in this place my thanks for this valuable as^: stance 



In the systematic arrangement, I shall follow Zittel's T j ~ ^ontology 

 (1880 and 1885), but for the Mollusca I shall use the English ^ition f 

 this work (Dall and Pilsbry, 1900). I regret very much that tl, e j a tter 

 did not come into my hands before the figures for the plates were 4 rawn 

 and sent to the printer, and this explains the fact that the arrange 

 of the species on the plates is different from that in the text. But I u 

 this will prove to be only a slight inconvenience, and will certainly k e 

 counterbalanced by the improvement in the systematic part of the text 





