368 University of California Publications in Geology [Vol. 8 



form (pi. 39, fig. 3) occurs in the lower part of the Upper San Pablo 

 group with the small, thick form of Astrodapsis tumidus. This form 

 appeal's to differ from that in the Lower San Pablo in that it has a 

 somewhat deeper notching at the ambitus in the ambulacral areas ; it is 

 thinner ; and the petals on some of the specimens have a tendency to 

 be slightly raised. Considering the paucity of material at hand, it 

 has not been deemed advisable to describe these forms as new varieties. 



Scutella gabbi Remond differs from Scutella oregonensis W. B. 

 Clark in that it does not show the posterior eccentricity of the apical 

 system, nor is the anus so strongly snpramarginal. Astrodapsis mer- 

 riami P. M. Anderson differs from Scutella gabbi in that it has a more 

 depressed test and possesses a more swollen margin. The form occur- 

 ring in the Astrodapsis tumidus zone closely resembles Astrodapsis 

 merriami found in the upper horizons of the "Vaqueros" formation, 

 in the posterior notching of the margin and in the tendency of the 

 petals to be raised, yet differs in that the odd anterior petal is raised 

 more than the others. 



Occurrence. — Typical and large forms are found in the basal beds 

 of the San Pablo group ; the notched form is from the Astrodapsis 

 tumidus zone of the lower part of the Upper San Pablo group. 



Average Measurements 





Typical form 



Large form 



Notched form 



Anteroposterior diameter 



25.3 mm. 



33.2 



28.7 



Transverse diameter 



26.3 



32.3 



26.5 



Greatest thickness 



6.3 



7.3 



6.0 



SCUTELLA GABBI Eemond, n. var. TENUIS 

 Plate 39, figure 4 



This form differs from Scutella gabbi Remond in that it is larger; 

 more strongly depressed ; the edge of the test is much thinner ; and the 

 notching of the ambitus in the ambulacral areas is deeper. 



It resembles Scutella fairbansli Arnold, but differs in its smaller 

 size and in that the rows of pores of the petals converge more closely ; 

 the ratio between the length of the petals and the distance from the 

 apical system to the ambitus is less in Scutella fairbanksi than in 

 Scutella gabbi, n. var. tenuis, but the ratio of the latter compared with 

 the same ratio in Scutella gabbi Remond shows a close resemblance. 



