58 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



distinct, subangular, but nut very prominent, concentric undulations, which 

 are separated \>y rather wide, shallow, rounded depressions. 



Length of the largest specimen hitherto seen, 10 inches; height of the 

 same, 9 inches. 



This species may be at once distinguished from I. A T ebra.scensis of Owen, 

 by its much more compressed, and more nearly circular form, as well as by 

 its less prominent and more flattened beaks ; which are also not so oblique, 

 and located farther back. The fact that the only two specimens of it yet 

 seen are both left valves, while those now at hand for comparison, as well as 

 that figured by Dr. Owen, of /. Nebrascensis, are light valves, led at first to 

 the suspicion that they might be the opposite valves of the same species. It 

 is manifest, however, that this cannot be the case ; for, in addition to the differ- 

 ences already mentioned, the specimens of the species under description are, 

 as above stated, distinctly more compressed than the right valve of I. Nebras- 

 censis, while in this genus the left valve is always the more convex, where 

 there is any perceptible difference. 



The specific name was given in honor of the lamented Lardner Vanuxem, 

 geologist of the third geological district of New York, and the discoverer of 

 the Cretaceous system in America. 



Locality and position — Same as the preceding. Collected by Lieut. 

 G. T. Balch, to whom we are indebted for the use of the specimens. 



Inoceramiis sublsevis, H. & M 



Plate 12, figs. 1, a, b. 

 Inoceramua nublwi'in, Hall anil Meek (1854), Mem. Am. Acad. Arts ami Sci., V (u. s.), 386, pi. 2, fig. 1. 



Shell of medium size, oval in outline, moderately gibbous, nearly or quite 

 equivalve, rather thin ; extremities rounded, base forming a broad, nearly 

 semicircular or subelliptical curve ; hinge apparently long and straight ; beaks 

 small, located near the anterior side, not much elevated above the hinge, nor 

 very distinctly incurved ; surface smooth, or only marked by very obscure, 

 concentric undulations, and fine, regular^equidistant lines of growth. 



Our larger specimens are too imperfect to give accurate measurements, 

 but some of them indicate a length of about 4.50 inches, and a height of 3 

 inches. This species will most generally be distinguished from the allied 

 forms in the Nebraska rocks, by the absence of distinct undulations, though 



