450 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



BILLINGSELLA Hall. 



Billingsella Hall and Clarke, 1892: Pal. New York, Vol. VIII, Pt. I, p. 230, PI. VII 

 A, figs. 1-9. 



Billingsella coloradoensis Shumard. 



PL LXI, figs 1, la-d. 



Orthis coloradoensis Shumard, 1860: Trans. St. Louis Acad. Sci., Vol. I, p. 627. 



Orthis pepina Hall, 1863 : Sixteenth Ann. Eept. New York State Cab. Nat. Hist., 

 p. 134, PI. VI, figs. 23-27. Hall, 1867: Trans. Albany Institute, Vol. V, p. 113. 

 Whitfield, 1S82: Geol. Wisconsin, Vol. IV, p. 170, PI. I, figs. 4, 5. 



Orthis f (Orthisina t) pepina Hall, 1883: Second Ann. Eept. New York State Geol- 

 ogist, PI. XXXVII, figs. 16-19. 



Billingsella pepina Hall and Clarke, 1892: Pal. New York, Vol. VIII, Pt. I, p. 230, PI. 

 VII, figs. 16-19; PI. YIlA, figs. 7-9. 



This species was described by Shumard, in 1860, as from the Potsdam 

 sandstone of the New York series, near the head of Morgans Creek, Burnett 

 County, Texas. He states that "the general form of the shell is very 

 similar to a species in my cabinet from the Potsdam sandstone of 

 Minnesota." 



In 1863 Professor Hall described a similar shell, from the sandstone 

 above Lake Pepin, Minnesota, under the name of Orthis pepina, stating that 

 when compared with Orthis coloradoensis from Texas the species is much 

 smaller, the length of the ventral valve is greater, and the stria?, are finer. 

 However, a comparison of an extended series of specimens collected in the 

 Upper Cambrian of Burnett County, Texas, leads me to believe that the 

 specimens from widely separated localities all belong to the one species 

 Billingsella coloradoensis. 



The size and form of these species appear to be remarkabl}" constant 

 wherever found, as is also the surface ornamentation, which consists of fine 

 concentric stria 3 and slender radiating costse, which are often unequal in 

 size. The concentric striae are unusually well shown in the material from 

 Texas, while the radiating costae are very faint. On specimens from the 

 St. Croix sandstone of Lake Pepin, Minnesota, the costa? and the concentric 

 stria? and lines of growth are strong and well shown in the casts of the 

 outer surface of the shell. The generic characters are finely shown by 

 specimens from the Gallatin Range in the Park, in which the characteristic 

 muscular scars of the ventral valve of Billingsella are well preserved; also 



