302 University of California Publications in Geology [Vol. 7 



slight tendency for the arch of the abactinal surface to flatten 

 near the lateral margins, but in most cases the profile of the 

 upper surface is regular between these margins. The slope of 

 the abactinal surface from the apex to the anterior margin is 

 rounded and rather abrupt, to the posterior margin flat and 

 gentle. There are neither lunules nor narrow marginal notches in 

 the posterior half of the test. The petals are almost closed, the 

 outer row of pores swinging in abruptly toward the inner row. 

 The posterior petals are slightly shorter as well as slightly 

 narrower than the lateral ones. Isolated pores are visible for 

 only one or two plates beyond the outer end of the petals. The 

 greatest width of the test is posterior to the center, and approxi- 

 mately through the apical system. 



Occurrence : Near Muir, Contra Costa County, California ; 

 in Kern County, California, on the north slope of the San Emig- 

 dio Mountains at the southern end of the San Joaquin Valley. 

 At the first locality only a single specimen has been found; at 

 the second the tests occur in great abundance. 



Known only in the lower half of the Miocene. 



Dimensions: Diameter through the anterior petal 53 mm.; 

 diameter between the lateral margins 62 mm. ; height 5 to 6 mm. 



Transmitted January 15, 1913. 



