70 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I26 



These three reservoirs will require no further investigation, either 

 because of immiment flooding or lack of productive exposures, unless 

 construction activities or other unusual circumstances unexpectedly 

 uncover significant remains. 



Several weeks were spent in both 1950 and 195 1 in the Canyon 

 Ferry area, which had been found to be unusually productive of small 

 mammals of Oligocene and Miocene ages. The investigations were 

 highly successful in that numerous individuals of forms only scantily 

 represented heretofore and a number of forms previously unknown 

 for the area were collected. During both years previously known 

 localities provided additional collections and in 1950 two new Miocene 

 fossil localities were discovered. A large number of jaws of a small 

 rodent of the genus Eumys were recovered. New or very rare forms, 

 for the area, include Peratherimn, an opossumlike marsupial of Oligo- 

 cene age; Cylindrodon, from the Lower Oligocene; and a shrewlike 

 insectivore of the Middle Oligocene. The excellent results obtained at 

 Canyon Ferry — in the expansion of the faunal assemblage of the 

 Oligocene and Miocene deposits and in the collection of large samples 

 of small mammals which will permit comparisons, from the stand- 

 point of environmental adaptation, with equivalent forms of the same 

 age in the Big Badlands of South Dakota — indicate the desirability 

 of exploiting this productive area as long as it is available. 



During approximately six weeks in 1950 and 1951, exposures of 

 the Paleocene Fort Union formation were explored in the Garrison 

 Reservoir area. In the lower part of the reservoir the remains of 

 vertebrates were found to be extremely rare, but it was possible to 

 make a number of collections of invertebrate forms. Farther up- 

 stream, vertebrates were more plentiful and the collections included 

 mammals, turtles, alligators, and fish. Several stratigraphic sections 

 were made and sediment samples for micropaleontological studies 

 were taken from various parts of the reservoir area. 



Only a rapid reconnaissance in the Oahe Reservoir area was made 

 in 1950, but during the next summer the Mobridge, S. Dak., vicinity 

 was inspected for four days and the lower end of the reservoir re- 

 ceived somewhat more protracted study. Satisfactory exposures were 

 not found near Mobridge, but in the Pierre area a nearly complete 

 skeleton of a pygmy mosasaur (Clidates pmmdis) and a number of 

 shark teeth were obtained from the Upper Cretaceous Pierre forma- 

 tion. Several weeks of work in 1950 and 195 1 in the Upper Creta- 

 ceous Pierre sediments in the Fort Randall Reservoir area yielded the 

 skull of a large plesiosaur, a marine turtle, and a fish, all from the 

 Oacoma Clay member of the formation. 



