I to 



University of California. 



[Vol. 2. 



Pliocene 



At the present time there are eight species of sea-urchins 

 know from the Neocene formations of California, all of which, on 

 account of their abundance and their good state of preservation, 

 were among the first fossil forms to be described from this coast. 

 They all belong to the Clypeastrida;, being distributed among the 

 genera, Echinaracknius, Scutella, Astrodapsis, and Clypeaster. The 

 species have generally been referred to the geological periods as 

 follows: 



Quaternary — Echinaracknius excentricus, Esch. 



( Echinaracknius excentricus, Esch. 

 i Scutella interlineata, Blake. 

 \ Astrodapsis Wkitneyi, Rem. 

 ' Astrodapsis tumidus, Rem. 



t'Astrodapsis tumidus, Rem. 

 I Astrodapsis Antiselli, Con. 

 Miocene -s Scutella {Clypeaster) Gabbi, Rem. 



I Echinaracknius (Scutella) Gibbsi, Rem. 

 \Clypeaster ? [Echinaracknius) Brewerianus, Rem. 



From the observations of the writer it appears that the geolog- 

 ical classification of these species, as indicated above, may not 

 be accepted without certain modifications, which are dependent 

 on the local classification of Neocene formations. In order to 

 discuss the subject intelligently it will be necessary first to notice 

 briefly the occurrence of the species individually. 



OCCURRENCE AND RANGE OF SPECIES. 



Echinaracknius excentricus and Scutella interlineata are both 

 found in the sea cliffs of Seven-mile Beach, south of San Francisco, 

 which have been referred to the Merced series (Pliocene). There 

 the first-named species occurs near the top of the section. If the 

 upper fossiliferous beds of the Seven-mile Beach section are Qua- 

 ternary, as many of the writers on the palaeontology of this series 

 (Remond*, Gabb|, Ashley J) have suggested, it will probably be 

 shown that E. excentricus does not occur there below the base of 



* Geol. Surv. of Cal. Geology, Vol. I, p. 79. 

 tGeol. Surv. Cal. Paleontology, Vol. II, p. no. 

 % Proc. Cal. Acad. Sc., Second Ser., Vol. V, p. 330. 



