Haynes: Fauna of the Upper Devonian in Montana. 39 



respects, but the ratio of width to height in Leiorhynchus dunbarense 

 is I : .6 instead of i : .9 as in L. astabulense, and the sides have fewer 

 plications. The type is in the Carnegie Museum. 



Locality. — Five specimens of this species were collected from the 

 limestone layers at the top of member number 5, near Dunbar's 

 mine, north of Three Forks. Three of them were collected by Dr, 

 Raymond in 1905 and two of them by the writer in 191 2. One very 

 well preserved specimen was obtained by the writer in 191 3 from the 

 base of gray limestone number 4, from east of Lombard, Montana. 



10. Leiorhynchus madisonense sp. nov. (Plate VII, figs. 11-13.) 



Outline of shell oval; width always greater than height; the ratio 

 varies from I : .64 to I : .76. An average specimen has a width of 

 19 mm. and a height of 14 mm., with a ratio of i : .73. 



The pedicle valve curves to the sides and has a well marked, rather 

 broad sinus, developed slightly above the middle of the shell. Beak 

 small and closely incurved over the umbo of the opposite valve. 



The brachial valve is much more convex than the pedicle, and 

 rounds to the sides. Mesial fold well-developed in most cases, and 

 greatly elevated at the outer border. Surface marked by fine im- 

 bricating concentric striae, also by fine radiating striae, which are well- 

 developed on the sides of the shell. The sinus is generally character- 

 ized by two rounded plications, rarely one or three. The fold is 

 usually marked by three, sometimes two, or four, plications. Sides 

 of the shell usually marked by one or two faint, low, rounded plications. 

 These plications all extend to the apex of the shell. The type is in the 

 Carnegie Museum. 



This species differs from Leiorhynchus mesacostale in the smaller 

 number of plications in the fold and sinus, and in the greater width 

 of the shell in relation to its height. 



Locality. — Specimens are numerous in the green shale and asso- 

 ciated limestone layers of member number 5, at Three Forks, Logan, 

 and most of the other localities in the region near Three Forks. 



II. Leiorhynchus madisonense var. gibbosum var. nov. (Plate VII, 



figs. 14-16.) 

 Cf. Leiorhynchus kellogi Hall, Pal. N. Y., Vol. IV, p. 361, PI. 56. 



Shell more gibbous and usually larger than Leiorhynchus madisonense. 

 An average specimen has a width of 23 mm. and a height of 20 mm., 



