448 DILLER AND STANTON THE SHASTA-CHICO SERIES. 



At the horizon just mentioned, about 2,000 feet below the top of the 

 Aucella beds, where A. piochii, var. ovata, is the most abundant form, the 

 first representatives of the second g-eneral group of forms of the type of 

 A. crassicollis, KeyserHng, occur. This includes all the broad, robust, 

 inflated forms in which both valves are ahnost equally convex and 

 nearly equal in size, such as the forms figured by Gabb * and referred to 

 Aucella piorhvi Aucellse of this type occur sparingly at the above-men- 

 tioned horizon, the lowest at which they have been observed, while they 

 are the dominant and almost exclusive forms in the upper 1,000 or 1,500 

 feet of Knoxville beds, only occasional specimens that can be referred to 

 Aucella piochii, var. ovata occurring with them. In Kussia, according to 

 Lahusen, all the Aucellse occurring in the Cretaceous belong to this 

 group. He recognizes the following species among them: Aucella crassi- 

 collis, A. crassicollis, ysiY. solida ; A.- crassicollis^ var. gracilis; A. huUoides, 

 A. Jceyserlingi, A. piriforviis and A. 'piriformis^ var. majuscula ; also A. 

 inflata from the upper Volgian, which is by most authors referred to the 

 Jurassic. Nearl}^ all of these forms can be duplicated in our collections 

 from the Knoxville beds, but as it does not seem possible to separate 

 these California specimens into definable species, they will be referred to 

 Aucella crassicolUs, Keyserling, which is the earliest valid name f that has 

 been applied to the group. 



Dr C. A. White and Mr J. F. Whiteaves in describing the American 

 Aucellse have both recognized the varietal importance of the two general 

 groups of forms here described. The facts as to their stratigraphic range 

 as we have now determined them justify their recognition as species, 

 even- though they are genetically related and connected by many inter- 

 mediate forms. 



It is an interesting fact that the various forms of Aucella have appeared 

 in this country in approximately the same order of succession that has 

 been determined by Lahusen for the Russian forms, though if, as we 

 believe, all the Knoxville beds are Cretaceous, they persisted longer here, 

 and each stage of development was considerably later. Lahusen states 

 that in Russia all the slender elongate species like Aucella mosquensls are 

 confined to the Jurassic, beginning with the striated A. bronni in the 

 beds with Cardioceras alternans. 



Other Knoxville Fossils. — The brief lists of fossils from the Bald Hills 

 region already given are sufficient to show the intimate connection of 

 the upper Aucella beds with the Horsetown. Other localities in the 



♦Paleontology of California, vol. ii, pi. 32, figs. 92a, 6, c. 



t Fischer de Waldheim in Oryctographie de Moscou first described and figured such forms under 

 the name Inoceramus concentricus, Parkinson. Subsequent authors, finding that Fischer's speci- 

 mens belonged to a different genus, as well as a different species, have quoted them as Aucella 

 concentrica, Fischer, a practice that is unjust as well as confusing. Lahusen has proposed the name 

 A. piriformis for the same specimens. 



