INVERTEBRATE I'ALyEONTt >L( )CY. 435 



mere variety, because it may yet prove to be specifically distinct from 8. 

 ( 'onradi. 



Locality and position. — Moreau River, Dakota; from the Fox Hills 

 group of the Upper Missouri Cretaceous series. 



Scaphit'es Nicolletii, Morton (sp.). 



Plate ;!4, figs. 4, «, /), c, and 2, a, b. 



Ammonites Nicolletii, Morton (1841), Jour. Acad. Nat. Sci. Philad., VIII, 209, pi. 10, fig. 3. 

 AmmoniUsNicolletii, Owen (1852), Report of U. S. Geol. Survey of Wisconsin, Iowa, and Minnesota, tab. 



viii, fig. 1. 

 Scaphites (Ammonitesl) comprimis, Owen (1852), ib., 580, tab. vii, tig. 4. 

 Scaphites NicolleM, Meek and llaydeu (1856), Proceed. Acad. Nat. Sci. Philad., VIII, 281.— Meek (1864), 



Smithsonian Check-List N. Am. Cret. Fossils, 24. 



Shell oval-subcircular, much compressed; volutions so deeply em- 

 bracing as to leave only a small umbilicus, all strongly compressed later- 

 ally, inner ones narrowly rounded on the periphery; deflected part of "last 

 turn so very short as not to become free at the aperture, narrowly flattened 

 on the periphery below, and somewhat widened and straightened along the 

 upper margin near the umbilicus; aperture narrow-oval; surface ornamented 

 by numerous small, somewhat flexuous costse, which increase by division and 

 intercalation so as to number about five times as many around the periphery 

 as at the inner side ; costse everywhere without tubercles or nodes, excepting 

 a single row along each side of the flattened periphery of the outer volution, 

 all crossing the periphery with a moderate forward curve. 



Length, 2.31 inches ; height, 1.92 inches; convexity, about 0.62 inch. 



The septa of this form correspond so nearly in their general features to 

 those of the last (as may be seen by our figures on plate 34) that the differ- 

 ences can be pointed out in a few words. In the first place, the terminal 

 divisions of its siphonal lobe are a little shorter, and show a disposition to 

 bifurcate, and the succeeding lateral pair of branches are proportionally a 

 little larger than in the last. Its first lateral lobe also differs in having its 

 body narrower, and its two terminal branches much more nearly equal, with 

 differently-formed subdivisions. Again, its second lateral lobe shows more 

 of a disposition to tripartite division, with more spreading branches. Its 

 third lateral lobe is much more decidedly trifid, and its fourth smaller and 

 less deeply bifid, while between the last and the umbilicus there are two 

 very small projections not seen in the last-described form. 



These differences in the details of the lobes and sinuses of the septa 



