408 A. HYATT TRIAS AND JURA IN THE WESTERN STATES. 



The Animonitinse associated with Aucella erringtoni are pecuhar species 

 of Perisphinctes and of other genera of the uppermost Jurassic more nearly 

 allied to the similar species of that genus found in the Aucella-bearing 

 rocks of central and northern Russia than those of any other fauna. The 

 uppermost Jura in Europe, Asia, India and South America is charac- 

 terized even Avhere no Aucellse have been found by the prevalence of 

 Perisphinctes, and we can now add North America to this list. 



Having, through the kindness of Messrs Diller and Stanton, been per- 

 mitted to study Ammonitin^e collected by them in the upper Knoxville, 

 I can now say that the fauna of the entire Gold belt series of slates have 

 nowhere been found to contain a species similar to those of the numerous 

 Ammonitina? found in the Cretaeic faunas of the upper Knoxville and 

 Shasta groups. The fact that some genera usually pass from the upper- 

 most Jura into the Cretaceous is of no consequence in this connection 

 and can be ignored. 



The only specimen about which I am now doubtful is that named 

 Olcostephanus (?) lindgreni. This shell has characteristics which might 

 occur in either an Upper Jurassic or early Cretaeic shell, but its nearest 

 congener appears to be one described as occurring in the youngest Jura 

 of Russia. The doubt in this case arises from the imperfect preservation 

 of the umbilicus and the importance of the characteristics thus obscured 

 or destroyed for the exact determination of the affinities in the shells of 

 this genus, the species of which occur both in the Jura and in the Cre- 

 taceous faunas of Europe. 



Aucella3 occur in the Russian faunas accompanied by Cardioceras 

 alternans (allied to our Cardioceras duhium) ; in the Oxfordian of central 

 Russia ; in the later horizons of the Jura further north, with a limited 

 number of Perisphinctes, and in the highest and j^oungest members of the 

 Jura in thick deposits, of which the Aucellse are almost the only fossils. 

 This is parallel with the history of the Aucellse-bearing rocks of California 

 as compared with those of Knoxville. Lastly, Aucellse of similar forms 

 to those of the plicated broad shells of Aucella piochi occur in the recog- 

 nized lowest Cretaeic faunas of Russia associated with numerous Am- 

 monitin?e of many genera, as they do in the upper Knoxville and Shasta 

 groups. 



I have referred above to the- similar relations existing between the 

 Alaskan species of Aucellse and some of these forms. Eichwald dis- 

 tinctly asserts the association of these Alaskan species with Ammonitinee, 

 but his text does not confirm this statement, since he gives no local lists 

 and makes nowhere any direct assertion that they occurred in the same 

 slabs with Ammonitinse. Grewingk did not find Aucella associated with 

 the species of Ammonitin?e that he collected, nor has Dall in his collec- 



