Haynes: Fauna of the Upper Devonian in Montana. 37 



hinge-line and relatively higher brachial valve than the specimens from 

 Iowa. Furthermore all the western specimens are more robust, and 

 have a ratio between the length of hinge and the maximum thickness 

 of the specimen which ranges from i : .86 to i : .54, while the same 

 ratios for specimens of Spirifer whitneyi from Iowa range from i : .5 

 to I : .46. 



A large percentage of the well-preserved specimens of Spirifer 

 whitneyi var. monticola, show fine striae on the rather broad, flattened, 

 radiating plications. The plications vary in number from thirteen to 

 twenty-nine on a side, and from nine to nineteen on the fold. The 

 size of a moderately small individual is: width 22 mm., height 25 mm., 

 height of area 5 mm., width of delthyrium .45 mm., thickness 19 mm. 

 The measurements of a rather large indi\idual are: width 37 mm., 

 height 30 mm., height of area 12 mm., width of delthyrium 9.5 mm., 

 thickness 26 mm. Specimens from the fissile green shales of number 

 5 are much better preserved than those from the limestone layers. 

 Almost all of the specimens from the shale show the characteristic 

 striations on the plications, and some show a tendency to develop, 

 alate, almost spiniform, hinge extremities.-- Such delicate spinose- 

 points are preserved in only a few of the specimens from the shale, sO' 

 that it seems likely that this is an abornmal feature and not a generaL 

 character. 



About fifteen of the specimens, including Nos. 174 a, b, and c, of the- 

 series just mentioned, and specimens numbered 172c and d,. 

 and 176 a and h, show under the hand-lens, or microscope, a spinose- 

 surface covering the plications. The character of this surface varies, 

 from numerous irregularly scattered small rounded spines, ^^ as seen 

 on specimens 172^ or 174a to elongate spine bases arranged in 

 radiating rows (See PI. V, figs. 7, 8, 9,), which under slight magnification 

 appear continuous, and therefore like the normal striae. Upon a closer 

 examination they appear to be an intermediate stage between the 

 normally striated specimens and the irregularly spinose individuals. 

 Since there is this gradation in surface character on specimens, which 

 in other respects are identical, it seems best to note it merely as a 

 variable detail in Spirifer whitneyi var. monticola. Specimens fromi 

 the green shale almost always have the details of the surface well- 

 preserved and it is from a study of these that the intermediate stages 



" See Plate V, fig. 6. 

 -^ See Plate V, fig. lo. 



