1920] 



Kew: Cretaceoiis and Cenozoic Echinoidea 



41 



species is evidently a primitive character and indicates an earlier 

 type of Scutella on the Pacific Coast. 



A number of species which seem more closely related to the pre- 

 Miocene forms, Scutella cooscnsis Kew and ^Si. newcomhei Kew, than to 

 the 8. merriami type are found in the Lower Miocene. One of the 

 best known is S. fairbanksi Arnold, occurring in a number of localities 

 in southern California. In general appearance, on account of their 

 large size and thin tests, the Lower Miocene forms resemble the earlier 

 Eocene and Oligocene species more than they do the more intimately 

 associated S. merriami type. The supramarginal position of the peri- 

 proct, one of the most characteristic features of *S'. fairbanksi, may 

 be a more specialized character, but in all the other forms of the 

 Lower Miocene it is marginal. The S. fairbanksi var. santanensis Kew, 

 found in the Santa Ana Mountains, seems to be somewhat more 

 highly developed in having marginal notches in the posterior ambu- 

 lacra. This form leads to the more deeply notched S. vaquerosensis 

 Kew, and later to the very irregularly shaped *S^. norrisi Pack through 

 the large gradational form of S. vaquerosensis. All of these forms 

 are not found in the same region nor in continuous stratigrapliic 

 series ; probably they are closely connected, and represent different 

 stages of development. *S'. fairbanksi has been reported from the 

 Sespe, lying below the Vaqueros, the formation in which all these 

 species are found. This suggests that 8. fairbanksi is the earliest form 

 of this group in California. In the section in which 8. vaquerosensis 

 occurs the smaller variety is near the base of the series of strata, 

 whereas the larger one is at the top. The exact stratigraphic occur- 

 rence of >S'. norrisi in the Vaqueros formation is somewliat doubtful. 

 In the discussion of the geographic ranges it is pointed out that this 

 species has a comparatively wide distribution ; this indicates that 

 it is a type having a high degree of specialization, which is of greater 

 importance than if it were a form with a limited distribution arising 

 from especially favorable conditions of segregation and environment. 



ASTRODAPSIS SERIES 



This genus, which is typically developed in the Miocene and 

 Pliocene strata of California, has given to us an almost complete his- 

 tory of its evolution. Its continuous stages are revealed by the great 

 number of specimens which have been obtained that show the develop- 

 ment of the genus from an early, simple, scutellid-like form to one 



