TURTLES OF JUDITH RIVER FORMATION 55 



collected by George M. Dawson near Milk River in Canada, from beds 

 referred by Cope to the ' Transition series, probably the Fort Union 

 or Lignite epoch,' but now known to belong to the Judith River." 

 This error is also perpetuated by Hay in his Fossil Turtles of North 

 America, 12 who, although obviously familiar with the original place 

 of publication, still gives the locality as "in the basin of Milk River, 

 south of Wood Mountain, Assiniboia, British Columbia." 



The above exposition would seem effectively to dispose of the 

 claim for Judith River age of the type material of Plastomenus 

 coalescens, though it might possibly be considered to figure as a 

 Judith River species if Doctor Hay's reference to it of a specimen 

 identified by Lambe as Trionyx vagans is of valid standing. That 

 is to say Lambe collected a large, finely preserved specimen, which 

 he identified as Cope's Trionyx vagans, in the Belly River deposits 

 in the region of the Red Deer River, below Berry Creek, in Alberta. 

 Concerning this Doctor Hay says : 18 "The present writer, regarding 

 Cope's type of Trionyx vagans as too small and imperfect a fragment 

 for satisfactory comparison with materials from any region, except 

 the type locality in Eastern Colorado, is compelled to seek for some 

 more probable disposition of Mr. Lambe's fine specimen. Since 

 the plastron of Cope's Plastomenus coalescens indicates a large tri- 

 onychid which lived in approximately the same region and in the 

 same geological period, it appears to be best to refer the Red Deer 

 River carapace to the same species." It appears, then, that the 

 study of these specimens themselves is not sufficient to determine 

 whether Lambe's specimen is really referable to Cope's species, so 

 the burden is placed on stratigraphy! 



4. Plastomenus costatus Cope. 



Type locality: "Bad Lands south of Woody Mountain, latitude 



49 °-". 



This species was found in the same locality and horizon as the 



last, and the same confusion and compounding of error has resulted. 



Simply because Woody Mountain was supposed to be in the valley 



12 1908, p. 489. 

 15 Op. cit., p. 489. 



