GEOLOGICAL SURVEY OF THE TERRITORIES. 311 



Compared with d'Orbiguy's figure and description of his V. fragilis, 

 given in the Palseont. Francaise, our shell differs in being regularly 

 rounded instead of truncated posteriorly. It is also straighter on the 

 basal margin, and more broadly rounded in front. In some of these 

 characters it agrees more nearly with Professor Zittel's figures, which I 

 suspect may represent a distinct species from that figured by d'Orbigny. 

 Still it differs from Professor Zittell's figures, in having its anterior 

 margin more broadly rounded, and its pallial margin straighter in out- 

 line. 



Locality and position: Mouth of Deer Creek, on North Platte, in 

 Wyoming Territory ; Fox Hills Group of the Upper Missouri cretaceous 

 series. 



LEPTOSOLEN CONRADI, (MEEK.) 



Shell elongate-oblong, nearly three times as long as high, moderately 

 convex; dorsal margin straight, pallial margin more or less nearly 

 straight, and subparallel to the dorsal, being a little convex in outline in 

 front of the middle, thence ascending obliquely forward to the narrowly- 

 rounded anterior end ; posterior margin truncated vertically, but 

 rounding abruptly into the dorsal and ventral borders above and below; 

 beaks not raised above the dorsal margin, and very inconspicuous, their 

 position only being indicated externally by the curves of the marks of 

 growth, located about one-third the length of the valves from the ante- 

 rior end ; surface only showing fine lines of growth. 



Length, 1.04 inches; height, 0.36 inch; convexity, 0.28 inch. 



Internal casts of this species show the impression of the strong 

 internal ridge; extending directly downward from the beaks, and grad- 

 ually dying out below the middle of the valves. These casts also show 

 the impression of a single small tooth in the right valve, just in front of 

 the upper termination of the deep furrow left by the strong internal 

 ridge. From these characters it is evident that this genus is allied to 

 Siliqua, Miihlfeldt (Leguminaria, Schum.), but differs, as pointed out 

 by Mr. Conrad, in having but a single hinge tooth in the right valve, 

 instead of three in each valve. It almost certainly includes Legumi- 

 naria Moreana, d'Orbigny (Pal. France Ter. Cret., Ill, PL 350, Figs. 

 8, 9, 10), and L. Petersi,' Reuss (Siliqna Petersi, Zittel, Bivalven der 

 Cos., jSTordostlieu Alpen, taf. 1, Fig. 3), both of which, like Mr. Conrad's 

 type, are cretaceous species. 



Compared with Mr. Conrad's typical species, L. biplicata (Siliguaria 

 Uplieata, Con., Jour. Acad. N. Sci., Ill, PI. 34, Fig. 17), our shell is seen 

 not only to be much smaller and proportionally shorter, but to differ in 

 not having the two broad prominences radiating forward and downward 

 from the beak of each valve, as in that species, though it shows a single 

 very obscure, broad prominence extending directly downward under the 

 beaks, and widening as it descends. In front and behind this there is also, 

 in each valve, a scarcely perceptible concavity. This broad prominence 

 also imparts a slight convexity to the outline of the base, just at the 

 point where the base in Mr. Conrad's species is sinuous. 



It is probably more nearly allied to Leptosolen Moreana, d'Orbigny 

 (sp.), already cited, but differs from d'Orbiguy's figure in being decidedly 

 straighter on the dorsal margin, and wider, as well as more distinctly 

 truncated posteriorly. Compared with Lept. Petersi, Eeuss (sp.), as 

 figured by Professor Zittel, our species will be readily distinguished by 

 having its internal ridge at right angles to the dorsal margin, instead of 

 extending obliquely backward and downward ; also in having its dorsal 



