664 SCIENCE PROGRESS 



taken in connection with the long, toothless rostrum, projecting 

 far in advance of the lower jaw and the weak state of the 

 dentition generally, suggest that these long-snouted dolphins 

 swam on the surface of the sea, where they captured their 

 food — probably fishes — in much the same manner as does the 

 skimmer among birds. In the same issue Dr. Abel also 

 describes the skull of Saurodelphis argentinus from the Argentine 

 Pliocene and shows that the genus was nearly allied to the 

 existing Amazonian genus Inia, of which it may have been 

 the ancestral form. 



Another dolphin related to Inia has been described from 

 the Patagonian Tertiary by Prof. F. W. True in vol. Hi. p. 441 

 of the Smithsonian Miscellaneous Collections under the name of 

 Proinia patagonica. The similarity in the form of the skull, 

 in spite of its imperfect condition, is stated to be sufficient to 

 indicate with certainty the near affinity of the extinct to the 

 modern genus. On the other hand, Proinia displays no 

 resemblance to the squalodonts, one of which occurs in the 

 same formation, thus throwing doubt on Dr. Abel's theory 

 of the derivation of the Iniidce from the Squalodontidce. In 

 the same article Mr. True describes a new specimen of the 

 skull of the Patagonian Prosqnalodon australis, a genus and 

 species first brought to notice by the present writer in 1894. 



That the South American ground-sloths effected an entrance 

 into North America during the later Pliocene or early Pleisto- 

 cene period has long been well known, but it is only by slow 

 degrees that we are learning the extent of their distribution 

 in that continent. The latest addition to the list of North 

 American ground-sloths is made by Prof. T. D. A. Cockerell, 

 who in vol. vi. p. 309 of the University of Colorado Studies 

 describes the skull of a mylodont from Walsenburg, Colorado. 

 In the absence of any evidence to the contrary this is referred 

 to the typical genus Mylodon, but without specific determination. 



The long-disputed question as to the systematic position 

 of the genus Plagiaulax of the Dorsetshire Purbeck and the 

 nearly allied North American Ptilodus appears to have been 

 finally settled by the discovery of a nearly complete skull and 

 parts of the skeleton of a species of the latter in the Fort Union 

 beds of Montana. Both Owen and Falconer regarded Plagiaulax 

 as a diprotodont marsupial, and this view was adopted by 

 the present writer in the Catalogue of Fossil Mammalia in the 



