110 University of California Pxiblications in Geology [Vol. 12 



Variations.—- A small thick form is characterized by a smaller 

 test, (average measurements: anteroposterior diameter 27.8 mm., 

 transverse diameter 24.6 mm., greatest thickness 8.6 mm.) ; in being 

 relatively thicker vv^ith a tumid margin ; and in having the superior 

 surface more evenly rounded in profile. Gradations may be found 

 between the typical Astrodapsis tumidus Remond and this form. 



Related forms. — Astrodapsis tumidus Remond is distinguished from 

 A. cierboensis (Kew) by its narrower and less closely constricted 

 petals, which are more strongly elevated, and in that it possesses 

 interambulacral depressions. The typical A. tumidus further differs 

 in having a tliinner margin. From A. major Kew it may be separated 

 by its smaller test; relatively' shallower interambulacral depressions; 

 in that the under surface is usually not so strongly concave ; and by 

 its comparatively thinner margin. The A. tumidus (small tJiick form) 

 has a relatively more elevated and more strongly convex upper surface. 

 It can be distinguished from A. alius Kew in that it lacks the dis- 

 tinctly conical test of the latter, and possesses interambulacral de- 

 pressions. A. whitneyi Remond can easily be separated from A. 

 tumidus Remond owing to its much thinner margin, narrower petals, 

 and by its distinctly bell-shaped appearance. Prom the Lower Etch- 

 egoin ( Jacalitos) species, A. arnoldi peltoides (Anderson and Martin) 

 and A. arnoldi (Pack), it is readily distinguished by the absence of 

 grooves in the ambulacral areas along the sides of the petals. It differs 

 from the former by having wider petals, and from the latter in being 

 of smaller size and in having relatively narrower poriferous areas in 

 the petals. 



Geologic li orison. — Specimens of the typical Astrodapsis tumidus 

 Remond are found abundantly in the lower part of the upper San 

 Pablo group in association with A. whitneyi Remond and A. altus 

 Kew. The small thick form occurs in the middle part of the Upper 

 San Pablo group, together with Scutella gahhi (Remond) [notched 

 form). Both forms are present in the upper part of the "Santa 

 Margarita" formation, associated with. A. whitneyi Remond and A. 

 ornatus Kew. 



Localities. — Type (Remond) and neotype (J. C. Merriam, 1899, 

 specimen no. 11329 Univ. Calif. Coll. Invert. Pal.) from south side of 

 San Pablo Bay. Also common in Mount Diablo region of Middle Cali- 

 fornia ; at the type locality of the ' ' Santa Margarita ' ' formation near 

 the town of Santa Margarita, San Luis Obispo County, California ; and 

 Carnaza Creek, and San Juan River district, San Luis Obispo County, 

 California. 



