Above is an enhanced image of the original illustration from Table VIII Figure 6 of the Ammonites opalus described in Illustrations to the Geological Report of Wisconsin, Iowa, and Minnesota by David Dale Owen Philadelphia: Lippincott, Grambo & Co. 1852. It is described as from the Cretaceous Formation of Nebraska Great Bend of the Missouri River, associated with Inoceramus Cripsii. Below is pattern on the shell.
Paul talks about the type specimen at The Field Museum (FMNH UC 6377) which is now called Rhaeboceras halli. John Evans a forward guide for the Owens survey expedition collected this specimen in 1849 which Owen described in 1852. The link to this video is at https://www.youtube.com/watch?v=RC7yCm4ue_I
The Equatorial Minnesota blog was helpful in researching this posting.
https://equatorialminnesota.blogspot.com/2017/04/david-dale-owen-first-mn-geological-survey.html
A scan of David Dale Owen's survey report can be found at:
https://archive.org/details/reportageologic00owengoog
