204 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Trigonia evansana Meek; Pectunculus veatchi Gabb, and 

 other species not identified, or not characteristic. This fauna 

 is rather contradictory and puzzling, so that in a former paper 

 (Smith, 1898, p. 138) the writer expressed the opinion that 

 either the fossils from that locality, but from different beds, 

 had not been differentiated in collecting, or that the strata 

 were transitional from Horsetown to Chico. A visit in 

 person to the locality, in the spring of 1899, enabled the 

 writer to find out definitely that there was only one fossil- 

 iferous bed; and the identification of two species oi Pla- 

 centiceras, the young stages of which were formerly supposed 

 by the writer to be Hopliies, place the Chico age, Ceno- 

 manian, of these beds almost beyond doubt. A still more 

 certain determination of the age of this species is given 

 by its occurrence, along with P. ^acificimi and a large 

 number of typical Chico species, in the Chico beds one- 

 half mile west of Henley, near Hornbrook, Siskiyou 

 county, California, where it was discovered by Mr. Frank 

 M. Anderson, to whose liberality the writer owes the use of 

 all specimens of P. californicum from that locality figured 

 in this paper. ^ 



During the summer of 1899 Dr. Stephen Bowers, of Los 

 Angeles, collected a number of Chico fossils in the San 

 Fernando mountains, Los Angeles county; these were sent 

 to the writer for inspection, and several specimens of P. 

 californicum were found among them. From its wide 

 range in northern, central, and southern California, always 

 in the same horizon, it is fair to assume that P. californicum 

 is characteristic of the lower Chico, or Cenomanian portion 

 of the formation. 



Poorly preserved young specimens of this species have a 

 certain resemblance to Schlmnbachia chicoensis, and have 

 been occasionally mistaken for it; but the young stages of 

 the two genera are so entirely different that a mistake is 

 hardly possible if one examines the inner coils. 



1 In the Proceedings of the California Academy of Sciences, 3d Series, Mr. Anderson 

 will describe this fauna in his monograph on the Cretaceous, and with his permission 

 the writer uses his manuscript name " Placentkeras califomictun Anderson." 



