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



changes in the total faunas, as well as they can be known 

 from the fragmentary collections that have been made and 

 studied, do not seem to warrant the assertion of a uniformly 

 transitional series, and perhaps this has not been claimed 

 Yet the breaks that had previously been conceived to exist 

 between the main divisions of the series were bridged over 

 or minimized by the passage across them of many impor- 

 tant forms. Thus it was left to be inferred that the transi- 

 tion from the Horsetown to the Lower Chico might not be 

 different from that between different parts of the Horse- 

 town itself, except perhaps locally. But our knowledge of 

 the fauna as a whole, of each of the different horizons 

 above named, has gradually become more complete by the 

 continual contributions that have from time to time been 

 made; and while it can not be called quite satisfactory, yet 

 on the whole it may be regarded as sufficient for at least 

 some general observations. It must be borne in mind, 

 however, that the Cretaceous species of California need a 

 revision before any final conclusions can be established or 

 an entirely reliable correlation made, based upon paleonto- 

 logical evidence. Much confusion has undoubtedly existed 

 in regard to the limits and range of certain species, that has 

 often resulted from laxness in the identification of species. 

 In the subjoined portion of this paper attention is called 

 to a few of the many corrections that are needed for a 

 more satisfactory treatment of the subject, and which a 

 successful treatment will demand. However, for the pres- 

 ent there are some general facts that may be clearly 

 established. 



2. Horizons Distinguished. 



The Chico Efoch. 



Regarding each division of the Cretaceous separately, 

 the fossil lists contributed by a number of its recognized 

 localities may be massed together, and by this means a 

 more complete idea of its general fauna can be gained than 



