ON DINOSAURIAN REPTILES FROM THE TWO 

 MEDICINE FORMATION OF MONTANA 



By Charles W. Gilmore 

 Curator of Vertebrate Paleontology, United States National Museum 



INTRODUCTION 



The Blackfeet Indian Reservation in northern Montana has been 

 the object of two expeditions by the Smithsonian Institution. It 

 was here in deposits of the Two Medicine (Upper Cretaceous) for- 

 mation that, in 1913, I discovered the type specimen of Brachycera- 

 tops inontanensis} The collections of this first expedition were 

 so promising that it was deemed highly desirable that the region 

 should be visited a second time. This desire was realized in 1928, 

 and the specimens described in the following pages are a part of 

 this latter collection, which, as a whole, adds considerably to our 

 knowledge of this meagerly known fauna and places it on a basis 

 where comprehensive comparisons with Upper Cretaceous faunas 

 of adjacent regions are now possible. 



The bulk of the collection will be described in a later paper, but 

 I have thought it advisable to record as soon as possible the discovery 

 of three genera new to the fauna, which include two new species. 



1. A NEW SPECIES OF PALAEOSCINCUS 



Among vertebrate fossils collected from the Two Medicine forma- 

 tion (Upper Cretaceous) of Montana, by a Smithsonian paleonto- 

 logical expedition in 1928, is a disarticulated skeleton of an armored 

 dinosaur displaying characters which indicate it to be an undescribed 

 species of the long established but little known genus Palaeoscincus. 



Palaeoscincus co8tatus{ founded by Dr. Joseph Leidy in 1856 on 

 a single tooth (pi. 4, fig. 3) was the first named North American 

 armored dinosaur. For more than half a century this remained a 

 genus of doubtful affinities, but with the acquisition by the American 



1 Gilmore, C. W., Prof. Paper 103, IT. S. Geol. Surv., 1917. 

 2Proc. Phila. Acad. Sciences, vol. 8, 1856, p. 72. 



No. 2839.— Proceedings U. S. National Museum, Vol. 77. Art. 16. 



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