314 GEOLOGICAL SUEVEY OF THE TERRITORIES. 



Length, 3.80 inches ; height, 2.20 inches ; convexity, 1.40 inches. 



This will be readily distinguished from that I have provisionally 

 referred to U. tellinoides, H., by its proportionally longer and more con- 

 vex valves, stouter hinge, and particularly by having larger, thicker, and 

 more prominent cardinal teeth, ranging vertically, instead of very 

 obliquely forward and downward. The specific name is given in honor 

 of Dr. Isaac Lea, of Philadelphia. 



Locality and position : Church Buttes, Wyoming Territory ; miocene 

 tertiary, in a rather coarse, greenish grit. 



UNIO WASHAKIENSIS, (MEEK.) 



Shell scarcely attaining a medium size ; thin, depressed, rather com- 

 pressed, longitudinally subovate ; anterior side short, rounded ; posterior 

 side long, with a narrowly-rounded or sometimes faintly sub truncated 

 extremity, the most prominent point being below the middle, while 

 above this there is usually an oblicpie slope from the posterior extremity 

 of the hinge; basal margin, forming a broad, semi-elliptic or semi-ovate 

 curve, in the latter case the most prominent part being a little in ad- 

 vance of the middle ; dorsal or hinge margin straight from the beaks to 

 the upper slope of the posterior margin ; beaks depressed nearly to the 

 dorsal margin, rather regularly convex, but not ventricose, and placed 

 about one fourth the length of the valves from the anterior extremity ; 

 umbonal slopes moderately and evenly convex ; surface smooth, or only 

 showing more or less distinct marks of growth, excepting near the im- 

 mediate points of the beaks, where well-preservecl specimens show 

 traces of minute, regular, longitudinal wrinkles, which terminate pos- 

 teriorly at two faint, oblique, obsolescent, linear ridges; hinge, slender; 

 cardinal teeth small, oblique, and apparently consisting of one in the 

 right and two in the left valve; lateral teeth straight, rather long, two 

 in the left, and one or two in the right valve. 



Length of a large specimen, 2.37 inches ; height, 1.26 inches ; convex- 

 ity, 0.72 inch. 



This species is related to U. priscus, M. & H., with which it agrees 

 nearly in form and surface characters. It is constantly smaller, how- 

 ever, and distinctly thinner, while its hinge is weaker and its cardinal 

 teeth smaller and much more oblique. The wrinkles on its beaks, and 

 the two oblique linear ridges on their posterior dorsal sides, are similar 

 to those on U. priscus, excepting that they are less distinctly defined 

 and occupy a much smaller space only near the points, instead of the 

 whole surface of the umbones, being in fact so obscure and so near the 

 points of the beaks as to be readily overlooked and entirely obsolete in 

 most cases. 



It will be distinguished from TJ. Haydeni mainly by its constantly more 

 depressed and more elongated form. Its stratigraphical position is also, 

 according to Dr. Hayden's observations, one thousand to two thousand 

 feet lower in the series than that of U. Haydeni. 



Locality and position : Washakie, Wyoming ; also on Henry's Fork 

 and on Green Eiver, Wyoming Territory, at all of which places it is as- 

 sociated with Viviporus paludinwformis (—Turbo paludinceformis Hall) 

 and Goniobasis nodtdifcra (=Cerithiuni nodulosum, Hall, not G. nodu 

 losa, Lea.) 



CORBICULA? PRACTA, (MEEK.) 



Shell attaining a rather large size, longitudinally ovate, wider 

 (higher) anteriorly, compressed, very thin and fragile ; anterior margin 



