1504 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



subgeneric name to Cyclomera* His type is a fragment of a subcylindrical 

 shell from the Cretaceous rocks of Texas, originally described by him under 

 the name Baculites annulatus.f I am not well enough acquainted, however, 

 with it to express any opinion of my own in regard to its relations to the 

 group of shells here under consideration. 



The genus Baculites resembles in form the genera Rkabdoceras, Ilauer, 

 from the Trias, and Baculina, d'Orbigny, with which types it also agrees 

 in the number of lobes and sinuses of its septa ; but it differs remarkably in 

 having these divisions deeply subdivided into digitate branches, instead of 

 being entirely simple. Consequently, it bears similar relations to these more 

 simple types that the Ay/imonitoid forms bear to Goniatites and Clidonites. 

 It is an interesting fact, however, that the very young Baculites, when not 

 more than 0.05 inch in diameter, has the lobes and sinuses of its septa very 

 nearly or quite as simple as those of the adult Rkabdoceras ;J and, from 

 analogy, we may infer that, in the very young Rkabdoceras, the septa will be 

 found nearly or quite without lobes or sinuses, and thus present the characters 

 of the old genus Orthoceras in this respect. 



So far as known, the genus Baculites is confined to the Cretaceous 

 system of rocks; the .Jurassic species referred to it by Quensteilt (B. 

 acuarius) belonging to the genus Baculina, d'Orbigny, while the few examples 

 originally supposed to have come from Tertiary rocks were subsequently 

 ascertained to belong to the Cretaceous. 



B « c II 1 i t e s O V a t U S , Say. 

 Plate 20, figs. 2, o, /*, rf, and 1, a, b. 



Baculites ovatus, Say (1821), Silliman's Am. Jour. Sci. and Arts, II, 41. — Morton (1829), Jour. Acad. Nat. 



Sci. Pbilad.,' VI, 196, pi. v, figs. 5 and ti ; and (1830) Am. Jour. Sci. and Arts, XVIII, 



24!>, pi. i, tigs. G,7, and 8 ; also (18:54) Synop. Org. Rem. Cre't. Group U.S., 42, pi. v, tigs. 



. r >, (>. — Hall anil Meek (1854), Mem. Am. Acad. Arts and Sci., V(n. s.), 399, pi. v.figs. 1 a, b, 



ami pi. vi, figs. 1-7. 

 Baculites bacillus, Meek and Ilayden (1861), Proceed. Acad. Nat. Sci. Pbilad., XIII. 442. 



Shell attaining a large size, elongated and rather gradually tapering; 

 section ovate, the antisiphonal side being more broadly rounded than I lie 

 opposite (or very rarely a little flattened '!) ; aperture of the same form as the 

 transverse section ; extension of the lip on the siphonal side long, tapering, 

 and narrowly rounded at the end : lateral sinuses of same deep, and about hall 

 in one-third the greater diameter of the shell ; antisiphonal margin of the lip 

 prominently rounded in outline; surface of young and medium-sized speci- 

 mens generally nearly smooth, while the uou-septate part of the adult shell is 



* Am. Jonni. Couch., II, 76, 18(i(i. t Proceed. Acad. Nat. Sci.. January, 1855, p. 265. 



! Sec .Mem. Am. Aead. Arts and Sci., Hoston. V (u. s. ), pi. \ i. 



