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44 University of California Puhlimtioms in Geology [Vol. 12 



(1) that characterized by A. major (Kew), which is the direct 

 descendant of the A. tumidus stock; (2) that characterized by A. 

 arnoldi (Pack), a descendant of A. antiselli; and (3) that by A. fer- 

 nandoemis Pack. Each of the three groups are marked by highly 

 developed astrodapsid features, such as very tumid petals and deep 

 interambulacral grooves. The presence of a new feature, the auxiliary 

 grooves along the sides of the petals, is noteworthy as a more advanced 

 character. A. major was confined to tlie San Pablo Bay-Mount Diablo 

 area, but in the southern San Joaquin Valley area the same stage of 

 evolution is represented b}^ A. arnoldi peltoides (Anderson and Mar- 

 tin ) . In the Salinas Valley province the second group was developing 

 at this time which liad tlie same general characters, though dii¥ering 

 in minor details, e.g., the petals are not so highly elevated and usually 

 narrower, and the test is usually less tumid. A. arnoldi arnoldi 

 gave rise to a variety, A. arnoldi var. dcpressus. Contemporaneous 

 witli A. arnoldi- arnoldi several other subspecies were present in 

 different parts of this province. These were A. arnoldi var. fresnoensis 

 Kew and ^1. arnoldi crassus Kew, which probably developed later into 

 A. ar)ioldi spatiosus Kew. The third group which was derived from 

 the A. tumidus stalk was A. fernandocnsis Pack. This group is char- 

 acterized by the presence of remarkably large tubercles, together with 

 the typical astrodapsid features. So far, only one species of this 

 group has geen recognized, occurring in Elsemere Canyon, near New- 

 liall, Los Angeles County. 



In the interval of time between the deposition of the beds con- 

 taining Astrodapsis hreiverianvs and those .yielding A. tumidus {small 

 th icli form ) , a group comparable to the groups had its start, viz., 

 the Astrodapsis whitneyi Remond group. The A. whitneyi group has 

 the raised petals, simple ambulacral furrows, and the inframarginal 

 position of the anus, which are true astrodapsid characters, yet the 

 A. whitneyi forms differ in having smooth interambulacral areas, a 

 much thinner margin, and a flattened submarginal area, giving the 

 test a bell-shaped appearance. An intermediate form is probably 

 A. alius KcAv, which has smooth interambulacral areas and a high, 

 conical test, the flat submarginal area not yet having been acquired. 

 This group not only developed in the San Pablo Bay-Mount Diablo 

 area but also in other parts of the state where the Upper San Pablo 

 (Santa Margarita) formation is present, with A. whitneyi as the one 

 species common to all localities ; the other species originating from the 

 same stalk were characteristic of defiuite geographic areas. 



