36 Annals of the Carnegie Museum. 



and the area. In cases where the striations are preserved on the 

 specimens from western America it is easy to refer them to the species 

 whitneyi, but the majority of the specimens are exfoliated, and they 

 therefore come within the limits of the species disjiinctus. This is 

 undoubtedly the reason why so many of the western American species 

 of this general type have been identified as Spirifer disjunctiis. The 

 wide variations in the European specimens of Spirifer disjunctiis = 

 Spirifer verneuili show that varietal diflferences have been overlooked 

 in the identification of the specimens. 



7. Spirifer whitneyi var. monticola, var. nov. (PI. V, figs. 6-10; 

 PI. VI, figs. 1-7). 

 Cf. Spirifer whitneyi Kindle, Bull. No. 391, U. S. G. S., p. 24, PL 8, figs. 2-5. 



By far the commonest of the specimens of Spirifer from Montana 

 is a robust form with a relatively short hinge-line. Several hundred 

 specimens of this variety were collected by Dr. Raymond and the 

 writer from all of the localities where the Three Forks Formation is 

 well exposed. These specimens are apparently identical with those 

 from the Ouray limestone of Colorado and New Mexico, which are 

 figured by Dr. Kindle and identified as Spirifer whitneyi. Dr. Kindle 

 notes the fact that the forms from Colorado and New Mexico are 

 more robust and have flatter and broader plications than the Iowa 

 specimens. He considers it undesirable to make a new species based 

 on these differences, because Spirifer disjiinctus is such a variable type. 



A study of the large collection of specimens from the Three Forks 

 formation has convinced the writer that these specimens show certain 

 characters which are sufificiently distinct from Spirifer whitneyi to 

 be the basis for a new variety, monticola. 



A series of seven specimens (See PI. VI) was selected to show varia- 

 tion in shape in the new variety. The ratios between the width and 

 height of the brachial valves are as follows: (a) .84 : i ; (b) .88 : 

 i; (c) .93 : i; (d) 1 : I- (g) I : .97; (e) 1 : .81; (/) i : .78. The ratios 

 of the width to the height of the area are as follows: (a) i : .152; (&) 

 I : .227; (c) I : 232; (d) I : .3; (e) I : .325; (0 i : .345; (g) i : .39. It 

 is interesting to note that with the exception of specimen, g, the 

 increase in the height of the area and its flattening-out follows directly 

 the increase in length of the hinge-line. 



A comparison of these ratios with those of Spirifer whitneyi from 

 Lime Creek show that all of the western specimens have a shorter 



