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University of Calif ornia Publications in Geology [Vol. 12 



the margin, where they are nearly twice the width of the interam- 

 bulacra ; the latter are widest opposite the ends of the petals and 

 become narrower at the margin. Inferior surface fiat to very slightly 

 concave. Peristome small, and approximately central. Periproct mar- 

 ginal to entirely supramarginal, small, and round. Ambulacral lines 

 weak and seldom seen ; they divide a short distance from the peristome 

 and continue nearly to the margin. 



Variations. — A large form is found near the base of the San Pablo 

 grouji which differs from the typical Scutella gabhi in being of larger 

 size and having a relatively more depressed test. In the Upper San 

 Pablo group a notched form occurs, which differs in having a some- 

 what deeper notching at the ambitus in the ambulacral areas. It is 

 slightly thinner, and the petals on some of the specimens have a 

 tejideucy to be slightly raised. 



Related forms. — Scutella gahbi is most closely related to S. mer- 

 riami (F. M. Anderson) ; but differs in that it has a more elevated 

 test ; does not possess the swollen margin ; lacks the greater tumidity 

 of the anterior odd ambulacral area ; and in that the periproct may 

 be more or less supramarginal in S. gabbi whereas in *S^. merriami it 

 is always marginal. 8. andersoni Twitchell is distinguished from 

 it, according to Twitchell, "....by its longitudinally ridged upper 

 surface, its longitudinally concave lower surface, and its pronounced 

 marginal notches opposite the posterior paired petals." According 

 to Pack, 8. fairbanksi Arnold, to which it is often compared, differs 

 considerably in "...attaining a greater size, in having a slightly 

 iindulating marginal outline, in having deeper and better marked 

 furrows on the actinal surface, and in having the anal pore entirely 

 upon the upper siirface. " Other differences show that the test is 

 relatively thinner, and that the petals do not extend so near the 

 margin. 



Geologic horizon. — Lower San Pablo group, Upper Miocene, asso- 

 ciated with 8. gabbi var. tenuis Kew. 



Localities. — Occurs "... abundantly on the eastern shore of San 

 Pablo Bay, south of Mare Island in soft sandstone of Miocene age" 

 (Remond). Neotype from Contra Costa County, California. 



Discussion. — Doubt is expressed by Twitchell as to the synonomy 

 of the Scutella gabbi described and figured by Merriam with that 

 described by Remond, in as much as a few dissimilarities occur in 

 the two descriptions. A great many specimens are at the writer's 

 disposal in the collections of the University of California, which have 



