1920] 



Keiv : 



Cretaceous and Cenozoic Echinoidea 



29 



The Cretaceous forms are mainly of the eassidulid and spatangid 

 types. Hemiaster seems to be the most characteristic form, no species 

 of this genus being reported from any later age. One species of 

 Catopygus{f) is present in the Upper Cretaceous, but this genus is 

 not confined to this horizon. 



The Spatangidae continue to be the dominant family in the Eocene, 

 the genus Schizaster making its appearance at this time and being the 

 most numerous throughout this period. Bhynchopygm, Spatangus, 

 and Cidaris are also found, but sparingly. Scutellid forms occur in 

 the Tejon group in both California and Oregon, though the ones 

 from the former locality are indeterminable. The occurrence of 

 Scutella in the Eocene is important in that it marks the first appear- 

 ance of this family on the west coast. 



The general character of the fauna of the Oligocene remains the 

 same as in the Eocene, the spatangids being represented by the genus 

 Schizaster. The genus Scutaster is the only scutellid which has been 

 reported so far and known to be characteristic of the Oligocene in 

 California, though Scutella newcombei Kew is present in the Sooke 

 beds of Puget Sound and S. blancoensis Kew from Oregon. 



The fauna of the Neocene consists almost wholly of scutellid forms, 

 of which three genera stand out more prominently than any others. 

 Each has a definite range and these overlap one another but little. 

 The Lower Miocene echinoids are composed almost entirely of 

 Scutellidae, only two species of Cassidulus and a single fragment of 

 a spatangoid having been found. The different character of the fauna 

 is probably due to the change in sedimentary conditions from those 

 hitherto existing. During the earlier periods the deposits mainly con- 

 sisted of fine-grained sandstone or shale, whereas in the early part 

 of the Miocene the coarse type of sediments point to the fact that 

 shallow water prevailed, in which the littoral forms such as seutellas 

 developed and not the deeper water spatangid types. Another feature 

 of the Miocene, and of the Pliocene also, is the marked rise in the 

 number of species and individuals of this group. In both the Vaqueros 

 formation or Turritella ineziana zone and the T. ocoyana zone of the 

 Monterey group, Lower and Middle Miocene, there are at least seven 

 different species or varieties, which represent the maximum develop- 

 ment of Scutella. Following the dominance of Scutella the genus 

 Astrodapsis makes its appearance. Altliough this genus was present 

 before the extinction of Scutella, the greatest development of Astro- 

 dapsis was during the decline of the former, that is, in the uppermost 



