.524 UX1TED STATES GEOLOGICAL SURVEY OP THE TERRITORIES. 



the casts of our type-specimens showing the hinge and muscular impressions 

 are not in a condition to illustrate these parts in a drawing very satisfactorily, 

 although sufficient for identification when directly compared, I have repre- 

 sented, by figure 9, b, of our plate 43, one of those from the Colorado locality. 

 This figure is natural size, and gives an accurate idea of the shell, excepting 

 that the hinge-margin is represented rather too thick, and the posterior 

 cardinal teeth are made to converge too abruptly to a point. The magnified 

 figure of the hinge of the same (fig. 9, c) gives a better representation of 

 this hinge, but makes the posterior cardinal tooth a little too narrow, and 

 does not show distinctly enough a little projection in the pit between it and 

 the middle tooth. • 



Of the specific identity of our type and the specimens from Colorado, I 

 think there can be scarcely any reasonable doubt. 



Locality avid position. — Brackish-water Lignite series of the age of the 

 Judith River or Fort Union group, on Cherry Creek, Dakota ; and appar- 

 ently from the same horizon on Bijou Creek, Colorado. 



Corbie ii la subeliiptica, var. Moreauensis. 



Plate 43, figs. 1, «, b, and •->. ■'. 



Cyrena Moreauensis, Meek and Hayden (1856), Proceed. Acad. Nat. Sci. Philad., VIII, 125. 

 Corbieula Moreauensis, Meek and Hayden (1860), ib., XII, 4:i'J. 



Since discovering that the type of the last-described species really 

 belongs to the transverse section of the genus Corbieula, and is not at all 

 related to Tellina, I have been led to compare the shells here under consid- 

 eration very carefully with if, and now believe that they may belong to a 

 more robust variety of the same species. The specimens of this shell yet 

 seen are not, it is true, in a very satisfactory condition for comparison, all 

 being more or less broken, and having the points of the beaks worn off; 

 while none of them show the pallial line. They evidently have the same 

 transverse form and general outline, the same character of hinge, muscular 

 impressions, surface-markings, and even show the same obscure internal 

 ridge extending downward from beneath the beaks. So there would seem, 

 as far as can be seen, little left to distinguish them but their larger size, 

 somewhat thicker and more convex valves, and perhaps rather broader hinge- 

 plate. Consequently, I am led to place them provisionally as a variety of 

 C. subeliiptica. 



Locality and position. — Moreau River, Dakota: from the same horizon 

 as t lie last. 



