Haynes: Fauna of the Upper Devonian in Montana. 35 



closely related to S. whitneyl than to 5. disjunctus, as was pointed out 

 by Dr. Kindle. The size of an average specimen from Montana is: 

 width 30 mm.; height 19 mm.; height of area 9 mm.; width of del- 

 thyrium 5.5 mm. 



6. Spirifer whitneyi var. gallatinensis, var. nov. (PI. V^ figs. 3-4; 



cf. PI. vni, fig. 12). 



About twenty-five specimens of the same general form as those 

 just described, show a very different type of area and on this account 

 have been described as a new variety, gallatinensis. These specimens 

 have a rather narrow area, which is usually flat, or only slightly curved, 

 although the beak of the pedicle may be strongly incurved. The area 

 is of equal width throughout its whole extent, and usually extends at 

 right angles to the hinge-line. The area generally shows distinct 

 fine vertical striae. 



The ratios of width to height of brachial valves range from i : .52 

 to I : .78. The ratios of width to height of area range from i : .125 

 to I : .2. The ratios of width to height of delthyrium range from 

 I : .8 to .9 : I. The size of an average individual is, width 29 mm.; 

 height 19 mm.; height of area 4 mm.; width of delthyrium 4 mm. 

 There are from sixteen to twenty-six plications on each side of the 

 shell, and from nine to fifteen bifurcating plications on the fold. Some 

 of the specimens show striations on the plications, and this and the 

 general shape of the shell indicates a close relationship with Spirifer 

 U'hitneyi. The type is in the Museum of Comparative Zoology. 



Some of the specimens of Spirifer disjunctus from Europe (locality 

 Try pres Walfourt) show a type of area with parallel sides similar to 

 Spirifer whitneyi var. gallatiyiensis. {Cf. PI. VIII, fig. 12.) Ratios 

 from the European specimens show a range in width to height of 

 brachial valve from i : .4 to i : .56, and a range in width to height 

 of area from i : .1 to i : .2, and a range in height to width of del- 

 thyrium from I : .62 to I : I. None of these specimens show traces 

 of striations on the plications. 



This close resemblance between certain specimens of Spirifer dis- 

 junctus from Boulonnais, and Spirifer whitneyi, and certain specimens 

 of Spirifer disjunctus from Try pres Walfourt and Spirifer whitneyi 

 var. gallatinensis shows that we have here a good example of parallel 

 development in two very similar species of spirifers. Each species 

 has developed similar variations in regard to the shape of the shell 



