I X V ERTEBEATE l'A hMi >XT< )L( )( 1 V. 



397 



Fig. 52 



between those of different individuals <>!' either form. Again, we sometimes, 

 though very rarely, meel with a specimen showing a still inure convex sec- 

 tion, as represented in the annexed cut. 



This latter form contrasts so strongly with the others that we were at 

 one time led to believe it a distinct species, and proposed for it the name 

 Pig- 61. B. baculus (Proceed. Acad. Nat. Sci. Philad., XITI, 445, 



1861). As I can. on a more critical examination, make 

 out no essential difference in the structure of its septa, 

 / however, from those of the other forms, 1 am now inclined 

 to think it only a variety of B ovatus, notwithstanding 

 its much more nearly circular section. I am the more 

 inclined to adopt this view, because, on comparison with 

 New Jersey specimens, generally' regarded as belonging to 

 l| /)'. ovatus, nearly, but not quite, as great differences of form 

 are found to exist among them. Mr. Conrad has also 

 described a very similar, though still more convex, form, 

 from the Cretaceous rocks of Mississippi, under the name 

 B. Spillmani (Jour. Acad. Nat. Sci. Philad., Ill, 334, pi. 

 35, tin 24) : hut as his specimen does not show the septa, 

 I have no means of making comparisons of internal struc- 

 ture. 



Locality and position. — This species has a wide geo- 

 graphical range in this country; hut no form figured from 

 foreign localities seems to belong properly to it. It is 

 common in New Jersey, Alabama, and at numerous locali- 

 ties in the Upper Missouri country*. Among the latter 

 mav he mentioned the Great Bend of the Missouri below 

 Fort Pierre, near the base of the Fort Pierre group; also, 

 in the upper beds of the same on Sage Creek and Chey- 

 Baculites omtus, var. c , m)e Ri ver an< J near (lie eastern base of the Black Hills, 



baculus. 



Pig. r>i. Section show- all in Dakota. It likewise occurs along the Missouri, 



lug its round-ovate between Fort Benton and Fort Union, and on the Yellow- 

 form. 

 Fig. 52. A side-view of stone River, in Montana, as well as at many localities 



>Ih'ii'.' "' Pai along the eastern base of the Rocky Mountains and else- 



where in Colorado. It ranges all through the Fort Pierre group, and up 

 into the Fox Hills beds of the Upper Missouri Cretaceous series. 



■ Say's type specimens coins from Monmouth County, New Jersey. 



