Baculites sp.
From the collection of Yale Peabody Museum. Free to download, adapt and use — no permission needed.
Geological context: Late Cretaceous, Marias River Sh, Kevin Mbr. Collection locality: limestone concretions below large septarian concretions, along W side of US Rt 15, & 6 miles SSW of Shelby, Toole County, Montana, USA. Collected by Neil H. Landman, Susan M. Kidwell, 1978. IP number 390833; lot count 1; accn=IPA.07111; associatedwith=on same slab: IP.852323,IP.390866,IP.390867,IP.390868,IP.390869,IP.390870,IP.390871,IP.390872,IP.390873,IP.390874,IP.390875,IP.390876,IP.390877,IP.390878,IP.852363,IP.852364,IP.852365,IP.852366,IP.852367,IP.852368,IP.852369,IP.852370,IP.852371,IP.852372,IP.852373,IP.852374,IP.852375,IP.852376,IP.852377,IP.852378,IP.852379,IP.852380,IP.852381.
Yale Peabody Museum’s own description