WHITE ON PALEONTOLOGY. 605 



Surface apparently simple, or, in other words, marked only by the 

 ordinary lines and imbrications of growth. 



Length of the largest example discovered 13 centimeters ; greatest 

 width of the same 7 centimeters. These proportions, and consequently 

 the marginal outline, vary somewhat with age, being opportionrally nar- 

 rower when young ; and, even in the case of adult specimens, the length 

 is sometimes proportionally less than that given above. 



This species resembles U. couesi White, with which it is associated, 

 in its great size, massive test, and simple surface ; but it differs in out- 

 line, being much narrower posteriorly, and in having its beak much 

 nearer to the front of the shell than it is in that species. It bears some 

 resemblance also to some of the varietal forms of U. dame Meek and 

 Hayden, but it is constantly a more massive shell, is always proportion- 

 ally wider in its widest part, and has its beaks placed farther forward, 

 the front in this species projecting only very slightly beyond them. 



The specific name is given in honor of Dr. F. M. Endlich, of the United 

 States Geological Survey of the Territories. 



Position and locality. — Wahsatch gronp ; — Black Buttes Station, Wyo- 

 ming Territory, M'here it is associated with the two foregoing species. 



Unio couesi White. — A very large, broad, arcuate-smooth species? 

 from the AVahsatch group at Black Buttes Station, Wyoming, was 

 described by me as Unio petrinus on page 125 of Powell's lleport on the 

 Geology of the Uinta Mountains, 1876. I had overlooked the fact that 

 Gould described a living species under the same name in the Proceed- 

 ings of the Boston Society of Natural History in 1855. I therefore 

 change the name of this species to U. couesi^ in honor of Dr. Elliott Coues, 

 the alile zoologist of the United States Geographical and Geological 

 Survey. 



Unio meeki White — The late Mr. F. B. Meek, in Dr. Hayden's 

 Report of 1872, United States Geological Survey of the Territories, 

 dedicated a species of Unio, from the Bridger group of Wyoming, to 

 Dr. Isaac Lea, of Philadelphia. Notwithstanding Mr. Meek's habit of 

 extraordinary carefulness, he seems to have overlooked the fact that 

 Gray had, some twenty years before, dedicated a Unio from China, 

 l)ublished in India, to Dr. Lea. It therefore becomes necessary to sub- 

 stitute another name for the fos.sil species, which I do by applying that 

 of my late distinguished friend. 



Unio mendax (sp. nov.). — Shell of medium size, elongate subelliptical 

 in outline, moderately gibbous; beaks placed somewhat near the front 

 end ; front regularly rounded down to the base, which is only slightly 

 convex or a little straightened ; dorsal margin slightly convex or nearly 

 straight and subparallel with the base ; posterior margin sloping 

 obliquely downward and backward from the dorsal margin, and ab- 

 ruptly rounded below to meet the basal margin. 



Surface marked only by the usual lines of growth, except that there 

 are usually numerous small wrinkles upon the beaks; and that two 



