408 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



pared lo concur. If Z?. anceps includes Morton's B. asper, however, the form 

 here doubtfully referred to the latter should also most probably be included 

 under Lamarck's name. 



That the shell here under consideration, as well as the others mentioned, 

 are all specifically distinct from Say's B. ovatus and B. compressus, I see no 

 reason whatever to doubt. The form here described agrees well in its 

 transverse section with B. ovatus, Say, and also presents no essential differ- 

 ences in its septa ; but it contrasts very strongly with that species in size, as 

 well as in other respects, being very much smaller, proportionally more 

 slender, more gradually tapering, and much more strongly undulated. Its 

 undulations also extend, well defined, farther downward upon the septate 

 part of the shell. That it is not the young of B. ovatus is clearly shown by 

 comparing it with specimens of that species of its own size, the latter being 

 always without lateral undulations, and decidedly more rapidly tapei'ing. I 

 have no doubt that this little shell represents the adult size of the species to 

 which it belongs. 



It seems rather questionable whether Lamarck's name B. anceps ought 

 to be retained, instead of B. dissimilis, Desmarest, which latter has priority 

 of date. Desmarest's name has been generally rejected, however, because it 

 was founded on the merely accidental condition of his type-specimen, which 

 had the undulations of one side worn off, so as to make its opposite sides 

 dissimilar. 



Locality and position. — Deer Creek, on the North Platte; from the Fox 

 Hills group of the Upper Missouri Cretaceous series. As generally under- 

 stood, Lamarck's species also occurs in New Jersey, Alabama, and perhaps 

 in Mississippi, and is likewise widely distributed in the Cretaceous rocks of 



Europe. 



ANCYLOCERATID^. 



Genus ANCYLOCERAS, d'Orbigny. 

 Synon.-Bam.ites (sp.), Sowerby and others; not Parkinson, 1811. 



Ancyhcems, d'Orbiguy (1841), Pale'ont. Fr. Terr. Cre"t., I, 491. — Agassiz and Desor (1842), Germ. 

 Trans. Sowerby's Min. Couch., 623. — Geinitz (184f>), Gruudr. d. Verst., 302 (as a sub- 

 genus under JJamites). — Meek and Hayden (1858), Proceed. Acad. Nat. Sci. Pbilad.,X, 

 56.— Chenn (1859), Man. Conch., 1,92.— Ooster (1860), Cat. Ceph. des Alpes Suisses, 

 part V, 5.— Meek (1864), Smithsonian Check-List N. Am. Cret. Fossils, 23.— Gabb 

 (1864), Palseont. Cal., I, 78; and (1869) ib., II, 138— Stoliczka (1866), PalsBont. Iudica, 

 I, 172.— Roemer (1870), Geol. von Oberschl., 281. 

 Ancylocerus, King (1844), Ann. and Mag. Nat. Hist., XIV (old ser.),278. 



Etym. — ayiii:}.or, curved ; ntpaQ, a horn. 

 Examp. — Ancyloceras Matlteronianum, d'Orbigny- 



Shell slender and elongated, with usually an oval section, the whole 



