628 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



Thracia? montanaensis (Meek)'? 



PI. LXXIII, fig. 10. 



Corimya montanaensis Meek, 1S73 : Ann. Kept. U. S. Geol. Surv. Terr, for 1872, p. 474. 



Shell small, subquadrate in outline, convex, with prominent beak situ- 

 ated a little in advance of the middle; dorsal margin nearly straight, 

 declining slightly on each side of the beak; anterior end broadly rounded, 

 forming almost a right angle with the dorsal margin above, and uniting 

 with the convex ventral margin below by a regular curve; posterior end 

 obliquely truncate; posterior umbonal ridge subangular and accompanied 

 by a narrow depressed area or groove; surface marked by lines of growth. 



Length, 17 mm.; height, 14 mm.; convexity of single valve, 4 mm. 



The above description is drawn from a single valve from "Devils 

 Slide, Cinnabar Mountain, Yellowstone River," which may be the original 

 type named by Meek in the report above referred to, though it was not 

 labeled by him. It was named in a list of fossils from this locality, with a 

 footnote saying that "This is very similar to some varieties of ft glabra 

 Agassiz, but it is a smaller, proportionately shorter, and more convex shell, 

 with the anterior margins just in front of the beak more excavated." 



Anatina (Cercomya) punctata n. sp. 

 PI. LXXIY, fig 5. 

 Shell of medium size, not so slender as the typical forms of the sub- ' 

 genus; beak prominent, somewhat in advance of the middle of the shell, 

 directed backward; dorsal margin almost straight and descending slightly 

 in front of the beaks, concave behind; anterior end broadly rounded, sub- 

 ano-ular above; posterior end much more narrow and rounded, ventral 

 margin slightly sinuous; surface of the shell divided into two distinct areas 

 by a narrow well-defined groove that descends almost vertically from the 

 beak to the ventral margin; anterior area marked by broad concentric 

 ridges and sulcations and by very fine lines of growth, the latter continuing 

 over the posterior area; middle third of the posterior area slightly more 

 convex and prominent than the rest and bearing about nine distinct granu- 

 lar radiating lines. In addition to this sculpture, which is seen on internal 

 casts, a mold of the exterior of the shell shows that the entire surface bears 

 radiating lines of minute tubercles, which are most prominent on the posterior 



