27 



of Montreal, geologist of the British American Boundary Commission, near 

 the line of the northern boundary of the United States (latitude 49°),. within 

 the drainage-area of the Milk River. The formations are regarded by him as 

 belonging to the Lignite or Fort Union of Dr. Hayden, and consist of green- 

 ish and greenish-brown arenaceous clays of various degrees of hardness, fre- 

 quently including small gravel-stones, and sometimes forming a hard cement 

 between them. The fossils were found near the base of the formation, and 

 "not more than one or two hundred feet above yellow arenaceous beds, which 

 I conceive represent Cretaceous No. 5, and which are rapidly followed in 

 descending by well-marked No. 4 with characteristic fossils." (Extracted 

 from letter of Mr. Dawson.) 



The species are the following : Clastes, sp.; Compsemys ogmius; C. ? victus; 

 Plastomenus costatus; 1 P.coalescens; Trionyx Ivagans; Trionyx ?sp.; ? Hadro- 

 saurus /sp.; Cionodon stenopsis. 



The dinosaurian remains are quite abundant, and indicate several species, 

 but are mostly so fragmentary as to be unfit for determination. The diagnos- 

 tic genera of this list are Co?npsemys, Plastomenus, and Cionodon; the species 

 referred to Hadrosaurus being represented by caudal vertebras only. The 

 first-named genus is characteristic of the Fort Union epoch only ; the frag- 

 ment referred to C. victus, the only species of the list previously known, is too 

 small for final specific reference. The Plastomenus coalescens is represented by 

 a more perfect specimen than any other species referred to this genus from the 

 Fort Union beds, but is not sufficiently complete to render the reference to 

 this Eocene genus final. It is, in any case, not a member of any other known 

 genus. One species of Trionyx is represented by a hyosternal bone, and is 

 not definable ; while the fragment referred to T. vagans, though closely 

 resembling that species, is not large enough for final determination. The 

 Cionodon, though based on incomplete remains, is quite sufficient for paleon- 

 tological purposes. 



In conclusion, it may be stated that there are present two genera in this 

 collection which are diagnostic of the Fort Union epoch, but no species cer- 

 tainly so, though two species are probably identical with species of that epoch; 

 also, that the presence of Dinosauria refers the fauna to the Mesozoic series; 

 and that there is no satisfactory evidence of the co-existence of these reptiles 



1 Two species aro provisionally referred to the Tertiary genus Plastomnims, but are too fragmentary for 

 final determination. 



