546 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



The identifications of this species are usually incorrect, the current type 

 of specimens differing markedly from the original description, which is 

 appended below. S. solidirostris Herrick 1 is an example of this, and the 

 form he has figured can not be included with White's type. 



"Shell rather small, nearly semicircular, wider than long, widest at 

 the hinge line, where it is sometimes extended into submucronate points, 

 rounded in front. 



Dorsal valve more convex from beak to front than transversely. Beak 

 scarcely prominent, slightly projecting beyond the hinge line. 



Ventral valve about twice as deep as the opposite one, regularly 

 arcuate from beak to front, but a little depressed near the cardinal extremi- 

 ties. Area large and well defined, foramen narrow, beak acute, incurved, 

 and becoming solidified as the foramen is progressively closed. Dental 

 plates strong, projecting a little forward of the hinge line. From six to 

 eight prominent plications on each side of the mesial fold and sinus, which 

 decrease regularly in size toward the hinge extremities. Sinus rather 

 broad and deep, distinctly defined even to the point of the beak. A 

 slightly elevated ridge extends along its bottom, and a corresponding 

 depression along the mesial fold. 



Mesial fold prominent and widely separated from the plications. 

 Surface marked by fine, lamellose, concentric striae, which arch upon the 

 plications and the ridge in the mesial sinus, and doubly arch upon the 

 mesial fold." 



White's reference of the species to Spiriferina. is undoubtedly correct. 

 Shells from the Madison limestone show the characteristic finely punctate 

 structure. 



Formation and locality: Madison limestone, east side of Gallatin River, 

 west of Electric Peak ; George M. Wright. Divide between Gallatin River 

 and Panther Creek, Gallatin Range ; amphitheater east of Bannock Peak, 

 Gallatin Range, bed 28 ; W. H. Weed. Crowfoot Ridge, Gallatin Range, 

 bed 26, bed 27, bed 31 ; J. P. Iddings and W. H. Weed. South of Forellen 

 Peak, Teton Range ; S. L. Penfield. West of Antler Peak, Gallatin Range; 

 Antler Peak, Gallatin Range ; A. C. Gill. Summit of peak west of Antler 

 Peak, Gallatin Range ; J. P. Iddings. South slope of Quadrant Mountain, 



'Herrick, 1888: Bull. Deuison University, Vol. Ill, p. 47, PI. II, tigs. 9-11; PI. V, fig. 13; also 

 Geol. Ohio, Vol. VII, PI. XXI, fig. 13. 



