416 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



mates Ancyloceras in form, almost the only difference being that in the latter 

 the coiled portion of the shell has its turns free instead of in contact. There 

 are, however, marked differences in the character of the septa of these types; 

 those of Ancyloceras having the lobes apparently invariably all divided into 

 unpaired parts. 



So far as known, the genus Scaphites appears to be confined to the Cre- 

 taceous system. In Europe, according to d'Orbigny, it commenced its exist- 

 ence during the deposition of the Ne'ocomien, or oldest member of that system 

 of rocks, and continued to the close of his division Ce'nomanien {Crate 

 Chloritee of some French writers) But, in this country, we find it well 

 represented in beds holding a considerably higher position, or apparently 

 corresponding to the true White Chalk of Europe. Some of the European 

 authors, however, have, since d'Orbigny's publications were issued, cited 

 species from the upper divisions of the Cretaceous 



Although not an especial generic, or even family, character, it may not 

 be out of place to mention the fact here that, as in Ammonites and some 

 other allied groups, those problematical bodies called Trigonellites (== 

 Aptychus) also occur, at least in sections of the genus Scaphites, as here 

 understood. 



The following remarks of the writer, cpioted, with modifications, from a 

 memoir on the Palaeontology of the Upper Missouri, published by the Smith- 

 sonian Institution in 1865, in the joint names of Meek and Hayden, will 

 serve to convey to the student some idea of the widely different views that 

 have been expressed in regard to the nature of these fossils. 



Few objects among all the relics of extinct life have been more puzzling 

 to the palaeontologist, or given origin to a greater diversity of opinions, than 

 these. Most of the early palaeontologists regarded them as the shells of 

 bivalve mollusks, as did Parkinson, Deslongchamps, and some later investi- 

 gators ; while others supposed them to be the palatal bones of fishes. Others, 

 again, maintained that they are the internal osselets of some extinct Cephal- 

 opod allied to Teudopsis ; and still others that they are an internal organ of 

 the animals that inhabited the shells in which they occur, analogous to that 

 connected with the digestive apparatus of Bulla and some other Gastero- 

 poda Burmeister supposed them to be external supplementary shell-pieces, 

 designed for the protection of the branchial sac when the animal was pro- 

 truded from the shell More recently, d'Orbigny, Pictet, and others have 



