94 IOWA GEOLOGICAL SURVEY 



superficial ornament is denuded, by means of the longitudinal 

 keel (text-fig. 15) which traverses the median line of the plate 

 for about three-fourths of its length. 



Formation and locality. Chemung group of Bradford county, 

 Pennsylvania, and Catskill of Delaware county, New York. Ac- 

 cording to Newberry, the same or a very similar species occurs 

 also in the Devonian of Belgium. 



Bothriolepis color adensis Eastman. 



1904. Bothriolepis color adensis C. R. Eastman, Amer. Jour. Sci. ser. 4, 18, p. 



254, text-figs. 2, 4. 

 1907. Bothriolepis coloradensis C. R. Eastman, Mem. N. Y. State Mus. 10 



p. 53. 



This, the largest known American species of Bothriolepis, is 

 chiefly interesting on account of its geographical and geological 

 occurrence, and for the evidence it furnishes regarding Aster- 

 olepid distribution. Considering that the genus is characteristic 

 of estuarine deposits in the Upper Devonian of all parts of the 

 world, it may be regarded as indicating the prevalence of Old 

 Red Sandstone conditions in the corresponding formation of 

 southwestern Colorado. The relations of this species seem to be 

 rather with the Canadian than with either of the Chemung-Cats- 

 kill forms occurring in the Atlantic Border States. Owing to 

 the absence, however, of Asterolepid remains in any intermedi- 

 ate Upper Devonian locality, although other Chemung forms 

 are present in abundance along the route, it is difficult to trace 

 a line of migration directly connecting the Cordilleran species 

 with those in New York and Pennsylvania. Assuming that the 

 former is a European immigrant across the Atlantic, if the pas- 

 sage were not by way of the Dakotan sea we must suppose it 

 to have entered either by skirting the land known as "Columbia" 

 to the south, or that which has been termed "Laurentia" on 

 the extreme north. The position of these Upper Devonic land- 

 masses is indicated in the map given in Plate XVI. 



Formation and locality. Elbert formation (Upper Devonian) ; 

 Rockwood and Devon Point, Colorado. 



