80 University of California PuMications in Oeology [Vol. 12 



(which in most specimens are very indistinct), and petals which reach 

 nearly to the margin, whereas Scutella is usually thin, with relatively 

 well developed ambulacral furrows and a wide submarginal area. 

 The genus later becomes more highly developed, the elevation of the 

 petals and the interambulacral depressions becoming more pronounced ; 

 finally in the Lower Etchegoin (Jacalitos) formation and the upper- 

 most part of the San Pablo formation a secondary set of grooves is 

 acquired, these being the depressions in the ambulacral areas along the 

 sides of the petals. The ambulacral furrows also become deeper and 

 with distinct branches near the margin, all extending on the upper 

 surface. 



The internal structure is similar to that of Scutella, having the 

 radial partitions in the interambulacral areas ; but, on the other hand, 

 it does not have the degree of complexity of the concentric pillars, 

 these being in some species, such as A. hrewerianus, poorly developed. 

 Moreover, in Astrodapsis the radial partitions do not extend nearly as 

 far in toward the peristome as in Scutella. 



ASTRODAPSIS ALTUS Kew 

 Plate 15, figures 4a, 4b 



Astrodapsis alius Kew. Univ. Calif. Publ. Bull. Dept. GeoL, vol. 8, 1915, 

 pp. 371-372, pi. 40, flgs. Za-Zh. 



Holotype.—'No. 10065 Univ. Calif. Coll. Invert. Pal. 



Test small. Average measurements : anteroposterior diameter 

 34.6 mm.; transverse diameter 31.5 mm.; greatest thickness 10.6 mm. 

 Subcircular to subpentagonal in outline ; margin thick ; superior sur- 

 face rising immediately from the ambitus to the summit, which is 

 comparatively high and anterior to the apical system, thus giving the 

 test a distinctly conical shape. Ambitus slightly notched in the pos- 

 terior ambulacral areas. Ambulacra petaloid ; petals slightly elevated 

 and wide open. Pores conjugate ; inner rows of rounded pores extend 

 to the margin in almost straight lines, converging but little; outer 

 rows of elongated pores converge close to the inner rows near the 

 margin, where they become rounded and continue parallel with the 

 inner rows to the ambitus. Interambulacral areas flat. Anus infra- 

 marginal. Inferior surface flat and lacking ambulacral furrows. 

 Tubercles small and set close together. 



