INVERTEBRATE PAL.EONTOLO( i Y . f) 1 7 



horizon of the Judith River beds; also at that horizon near the mouth of 

 Judith River, Montana. The type-specimen from the Yellowstone is repre- 

 sented by our figure 8, d, of plate 43; while the other specimens from near 

 the mouth of Judith River are represented by figures 8, a, b, c, of the same 

 plate. Figures 8, a, and 8, b, were made out by tracing the lines of growth 

 near the umbones of imperfect larger specimens, to get the outlines of young 

 shells of the sizes represented. 



I it i o Dana;, M. & H. 



Plate 41, (i^s. 3, a, b, c. 

 Unio Dana, Meek and Haydeu (1857), Proceed. Acad. Nat. Sci. Philad., IX, 145. 



Shell transversely elongated, or with length more than twice the height, 

 moderately convex, thick, arcuate ; anterior side rounded; base most prom- 

 inent in the anterior region, distinctly sinuous at or a little behind the middle ; 

 posterior side long, narrow, and rather narrowly rounded at the extremity; 

 dorsal margin declining with a long, gently convex outline, from near the 

 beaks posteriorly, and sloping or rounding much more abruptly in front; 

 beaks depressed, oblique, located nearer the anterior extremity than the 

 middle; ligament very long; flanks more or less concave from the most 

 arched part of the base, obliquely up toward the umbones; surface (the 

 epidermis being always removed) marked by rather distinct lines of growth, 

 and, on the exposed laminae, obscure radiating stria 3 . 



Length, 3.30 inches; height, 1.48 inches; breadth, about 1.13 inches. 



The only specimen yet seen, showing the hinge, is a left valve, in 

 which the posterior cardinal tooth is rather prominent and somewhat com- 

 pressed, and the anterior one smaller. The lateral teeth are very long and 

 laminar, while the cicatrices are deep and distinctly corrugated. The beaks, 

 in all our specimens, are too much worn and exfoliated to show whether they 

 were concentrically wrinkled, though they seem not to have been. 



In speaking of this and the following species, Mr. Lea, to whom we sub- 

 mitted our specimens, remarked that '•(hey are all characterized by an 

 obliqueness not usual in the genus. The beaks are nearly terminal in all of 

 them, and they have a general massive character, which causes a disposition 

 to enlarged cardinal and lateral teeth. This enlargement is more particu- 

 larly noticeable in the cardinal teeth, which are all massive and very much 

 corrugated. It is evident from the deep corrugations of the great cicatrices 

 that the muscular power of the animal was very great." 



