504 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



Formation and locality : Three Forks limestone, south slope of Antler 

 Peak, Gallatin Range ; south side Soda Butte Creek, northwest of Abiathar 

 Peak, Absaroka Range ; J. P. Iddings. North side of saddle west of Mount 

 Miller, Absaroka Range; Louis V. Pirsson. Near Otterville and Sedalia, 

 Missouri. 



SPIRIFER Sowerby, 1815. 



Spirifer engelmanni Meek. 

 PI. LXVI, figs. 3a, 3Z>, 3c, 3d. 



Spirifera engelmanni Meek, 1800: Proc. Acad. Nat. Sci. Phila., p. 308. Meek, 1877: 

 King's U. S. Geol. Expl. 40th Par., Vol. IV, p. 41, PI. Ill, figs. 3-3a, 



Spirifer engelmanni Meek, 1876: Simpson's Kept. Espl. Gt. Basin. Terr. Utah, p. 340, 

 PL I, figs, la-lc. 



There is only one example of this species. Though otherwise appar- 

 ently identical with the smaller forms of S. engelmanni, it is abnormal in this, 

 that the strong plication bounding the sinus bifurcates, the two inner ribs 

 lying upon the sides of the sinus. 1 have not observed this in S. engelmanni 

 from Nevada, but have seen dorsal valves with a shallow median sulcus on 

 the fold, so that there is little reason for believing that such irregularities 

 do not occur on the other valve as well. The specimen could scarcely be 

 a young individual of S. disjunctus, for that species has finer plications, 

 which are distributed in large numbers on both fold and sinus. 



Formation and locality: Three Forks limestone, south side Soda Butte 

 Creek, northwest of Abiathar Peak, Absaroka Range; J. P. Iddings. Middle 

 Devonian, Neils Valley, Utah; White Pine District, Nevada. 



ATHYRIS McCoy, 1844. 



Athyris vittata var. triplicata n. var. 



PI. LXVI, figs. 4a, ib, 4c. 



Shell small, subcircular. The two valves moderately and equally 

 convex. Ventral valve marked by a broad, shallow median sinus. On 

 either side is a faint sinuation separated from the median one by a sharp 

 ridge. Dorsal with well-defined, square fold, bounded on either side by an 

 angular depression, after which follow, one on each side, two other slight 

 folds. All the plications of this shell are discernible for only a short 

 distance back from the margin. Width, 9 mm. ; length, nearly the same. 



