192 University of California Publications in Geology [Vol. 10 



PAGE 



Summary : 227 



Occurrence of Etchegoin species by localities in the Coalinga region 227 



Description of Etchegoin invertebrate localities 228 



Description of species 231 



Anodonta nitida, n.sp 231 



Pecten egregius, n. sp 231 



Pecten proteus, n.sp 232 



Maeoma inquinata affinis, n.var 233 



Semele fausta, n.sp 233 



Thracia formosa, n.sp. 234 



Fissuridea unica, n.sp 234 



Tegula (Chlorostoma) pulcella, n.sp 235 



Chrysodomus packardi, n.sp 235 



Murex concinna, n.sp 236 



Murex tethys, n.sp 236 



Trophon belcheri avitum, n.var 237 



Cancellaria crassa, n.sp 237 



Cancellaria fernandoensis tribulis, n.var 238 



Pecten etchegoini Anderson 239 



Serpula (?), sp 239 



Cancellaria rapa, n.sp 240 



INTRODUCTION 



The Etchegoin group of California has for a number of years 

 attracted the attention of palaeontologists and geologists because of 

 its somewhat uncertain position with respect to the other divisions of 

 the late Tertiary. Especially has it been difficult to ascertain the time 

 relation between these beds and the Pliocene sections along the outer 

 side of the Coast Ranges south of San Francisco. The Etchegoin has 

 been considered the equivalent of the San Pablo Miocene by certain 

 writers, while by others it is held to represent the stage of the Purisima 

 and Merced Pliocene. Although excellent work has been done on the 

 Etchegoin invertebrate fauna by several investigators, the difficulties 

 of pioneer work have made it impossible to secure the large represen- 

 tation now available to the writer. The determination of the age of 

 this group has recently been facilitated by the finding of remains of 

 land mammals at several horizons in a predominantly marine section. 

 The Etchegoin has come, therefore, in many ways to have unusual 

 significance in the consideration of the problem of the later Tertiary 

 of middle California. 



Due to the peculiar local character of many of the Pliocene deposits 

 of the Pacific Coast, correlation by lithology, except for very short 

 distances, becomes extremely hazardous or impossible. For the ex- 



