Since the preparation of the paper on the “Aftonian mammalian fauna,” which was published in October, 1909,2 a large amount of new information and new material has been received. Our knowledge of the surprising volume and geographic distribution of the Aftonian gravels has been greatly extended during the past two seasons by the field work of Shimek, who has devoted much time to the study of the problem and has noted and recorded the occurrence of true Aftonian deposits at short intervals over a wide belt, reaching from Sioux Falls, South Dakota, to Rockport, in northwestern Missouri. There are reasons for believing that the area studied includes but a mere fraction of that in which fossil-bearing Aftonian beds are distributed. Aftonian deposits are found on both sides of the Big Sioux and Missouri rivers; they are known in Muscatine County and a number of other localities on the Mississippi, . . .