INTRODUCTORY Rt^MARKS. 9 



tiitcs, etc., directly associated witli the more ancient genus Orfhoceros. 

 There have also been found in these beds the following specks, closely allied 

 to, or possibly in some cases identical with, Ilalobia Lommelei, Monotis 8ali- 

 narius, Ccratifes Ilaidingcrii, Archcstes Aiissceairiis, etc. There are likewise 

 known from this formation various other types of the Ammomt'uhp, which, 

 like those found at the same horizon in Europe, are not true Ammonites, nor 

 Ceratites, nor yet Goniatites, as these genera have been restricted 1)y late 

 authors, but new generic types, sometimes intermediate in their characters 

 between the typical forms of the above-mentioned genera. 



It is evident, from the collections that have been already obtained 

 fi'om this formation, that a rich harvest of new and interesting fornis awaits 

 the collector who can visit this region under circumstances favorable to its 

 thorough exploration. 



The species in the collection believed to be of Jurassic age are 

 illustrated on plate 12. The specimens of Bekmnitcc. came from the West 

 Humboldt Range, Nevada ; while all of the others wei^e collected four or 

 five hundred miles further eastward, at Weber Canon, Wasatch IJange, 

 l^tali, from apparently about the same horizon. It is barely possible tljat 

 a fcAv of the West Humboldt species that have been supposed to l)e of 

 Triassic age may belong more properly to the Jurassic (Lias), as there 

 seems to be a great development of these rocks there, without a strongly- 

 marked division, so far as lithological characters are concerned, if we can 

 judge by the matrix of the specimens. At any rate, the specimens of 

 Bclemrtites from there are contained in an apparently undistinguishable 

 matrix from that of the OrtJioceras and other Triassic forms; while Mr. 

 Gabb has described from that region an Ammonite (specimens of which I 

 have seen in a similar matrix) that seems scarcely distinguishable from the 

 European low Liassic species A. hisxdcatus. 



The species figured on the lower half of plate 12, fi'om Weber Canon, 



have been placed together in a separate division, because some douljts at 



one time existed in regard to the stratigra])hical position of the bed fniui 



which they were obtained.* 



* Since this was written and tlio plates arranged, Mr. King informs me that lie 

 lias fonnd this rock to be, as I bad from the lirst believed, of Oarbouifeious age. — F. 

 15. M., Nov. 29, 1874. 



