30 University of California Publications in Geology [Vol. 12 



Miocene (upper part of the San Pablo group). After this period the 

 reduction in the number of species was rapid; we have a decrease 

 from at least fifteen forms in this formation to seven in the Pliocene, 

 Lower Etchegoin (Jacalitos) formation. The next important genus 

 to make its appearance is Dendraster, which invaded California seas 

 in Lower Pliocene time, during the decline of Astrodapsis. The 

 Upper Pliocene formations show the greatest development of the 

 dendrasters, when at least twelve forms are represented. After the 

 close of tlie Pliocene there is a rapid decline in the number of species 

 until at present the widely distributed D. excentricus (Bschscholtz) 

 is the only living species. 



Of the less important genera, Sismondiai?) is reported by 

 Twitchell to occur in the LTpper Etchegoin formation ; Strongylocen- 

 trotus is not found earlier than the Pliocene of Southern California 

 and is very abundant in the Pleistocene along the Pacific Coast at 

 present; BhyncJiopygus is present in the Lower Miocene, continuing 

 from the Eocene ; Mcllita occurs in the Pleistocene Upper San Pedro 

 formation, but is now extinct on the coast of California ; and Trip- 

 neustes, Clypcastcr, and Encope are found in the Pliocene, Carrizo 

 Creek formation, but belong to the Gulf of California province, which 

 contains a fauna distinct from that of the Pacific Coast proper. 



GEOGRAPHIC DISTRIBUTION 



Although a great mass of sediments was deposited during the 

 Cretaceous, which are preserved to us in a large part today, we find 

 in them an extraordinary lack of fossil echinoids. This fact is still 

 more striking, considering the large collections of invertebrates that 

 have been made from the same formations in many parts of the 

 state. Very little is known about the Lower Cretaceous echinoderms, 

 for the Tesla district of Middle California is the only locality in which 

 any have been collected up to the present time. In the Upper Cre- 

 taceous they were more numerous, both in species and individuals, 

 and in geographic distribution are known to have lived along the 

 coast from the Santa Ana Mountains of Southern California to the 

 northern j^art of the Sacramento Valley. Hemiaster californicus 

 Clark has been found in both localities, indicating one of the most 

 extensive ranges for any west coast echinoid. From the data con- 



