1922] Trash: The Briones Formation of Middle California 139 



FAUNA 



The Briones formation is here treated as a unit. Sufficient collec- 

 tions have not been made to warrant the determination of minor f aunal 

 zones, if any occur. 



There are several forms which are regarded as characteristic of 

 the Briones formation. The most characteristic is Astrodapsis 

 breiverianus (Remond), which is quite common. In fact, for several 

 years previous to the application of the name Briones, the term 

 ' ' Scutella breweriana zone ' ' was applied to these beds. 



Other good markers are : 



Astrodapsis brewerianus diabloensis Kew 



Pecten ricei, n. sp. 



Koilopleura sinuata (Gabb) 



Trophon daviesi, n. sp. 



Modiolus gabbi subeonvexus, n. var. 



Modiolus veronensis, n. sp. 



The following species complete the list of those forms so far recog- 

 nized only from the Briones. An asterisk indicates that the species is 

 of relatively rare occurrence. 



Siphonalia rodeoensis, n. sp. 

 *Antigona willisi, n. sp. 

 *Leda furlongi, n. sp. 

 *Pecten andersoni gonicostus, n. var. 



Pecten tolmani Hall and Ambrose 

 *Pecten vickeryi, n. sp. 



Spisula faleata brioniana, n. var. 



Tivela merriami, n. sp. 

 *Venus brioniana, n. sp. 

 *Calliostoma obliquistriata, n. sp. 

 *Ficus rodeoensis English 

 *01iva simondsi, n. sp. 

 *Sinum trigenarium, n. sp. 



Pecten raymondi brionianus, n. var., is also very common, but it is 

 not restricted to the Briones, for occasional specimens are found in 

 the San Pablo. In the absence of other reliable markers, the finding 

 of a preponderance of this variety may be taken as a fair indication 

 of the Briones age of a formation. 



Nassa tvhitneyi, n. sp., is also an abundant species in the Briones. 

 As yet it has not been found in the San Pablo. Hence it may serve 

 as an aid in distinguishing the Briones from the San Pablo (Cierbo 



