468 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



toupee, Roeiner. Thai both Roemer's .species and the Indian form referred 

 by Dr. Stoliczka to A. Guadaloupee are clearly distinct, I have no doubt 

 whatever; and I think Dr. Stoliczka would have readily concurred in this 

 opinion had he been well acquainted with the latter. It seems to me also 

 very doubtful whether his Indian shell is identical with A. Guadaloupee. It 

 is evidently much more nearly related to A. syrtalis, Morton, though it pre- 

 sents marked differences in the form of the siphonal lobe, which lias its two 

 branches very slender, and projecting obliquely from the aides of its body, 

 instead of being broader and terminal, as in A. syrtalis, Morton, represented 

 in our cut No. 66, from Morton's type-specimen. 



Locality and position — Dr. Dekay's type-specimen of this species came 

 from the Cretaceous Greensands of New Jersey. It also occurs at the same 

 horizon on the Chesapeake and Delaware Canal in the State of Delaware: 

 and has likewise been found in the States of Texas, Alabama, and Tennessee. 

 The small specimen figured on our plate 24 came from Cheyenne River, 

 Dakota; where it occurs in the Fort Pierre group of the Upper Missouri 

 Cretaceous series. Specimens nearly two feet in diameter, as well as oi 

 smaller sizes, have also been found on Bear Creek, a small tributary of Chey- 

 enne River. The large specimen from which our cut No. 65, of a septum ol 

 this species was drawn, came from North Red River, Minnesota. I have 

 also seen a specimen of it in Professor Hind's collection, from Saskatchewan 

 River, British America. 



Plaeenticeras placenta, v a r . intercalare. 



Plate 23, figs. 1 , a,h,c. 



1 Ammonites syrtalis, Mortou (1834), Synop. Org. Rem. Cret. Grpup U. S., 40, pi. xvi (xiv by mistake), fig. 



iv— Gabb (1861), Synop. Moll. Cret. Form., 17.— Meek (1864), Smithsonian Check-List 



N. Am. Cret. Fossils, 25. 

 Ammonites placenta, var. interealaris, Meek and Hayden (1860), Proceed. Acad. Nat. Sci. Philad., XII, 117. — 



Gabb (1861), Synop. Moll. Cret. Form., 15.— Meek (1864), Smithsonian Check-List, 25. 

 ? Ammonites Tamulious, Blansford (1862), Mem. Geol. Surv. India, IV, 118 (without figure or description), 

 f Ammonites Gitadaloupa; Stoliczka (1865), Pnlseont. Indica, I, 90, pi. xlvii.tigs. 1 and 2; also pi. xlviii, 



tig. 1 (not Roemer). 



Shell attaining a large size, lenticular in form ; umbilicus small; volu- 

 tions with greatest convexity near the inner side, about three-fourths the 

 breadth of each inner turn embraced within the deep sinus at the umbili- 

 cal side of the next succeeding outer one, all with sides converging, wifli 

 slight convexity, from near the umbilical margin to the very narrowly-trun- 

 cated and slightly concave periphery, which is bounded on each side by a 



