136 University of California Puhlications in Geology [Vol. 12 



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 jiosterior to the center, and 

 ajjproximately through the apical system. 



Geologic horizon. — Uppermost Oligocene. 



Localities. — Holotype from near Muir, Contra Costa County, Cali- 

 fornia, Univ. Calif, loe. 424. Figured specimen from north slope 

 of San Emigdio Mountains at southern end of San Joaquin Valley, 

 Kern County, California ; occurs abundantly at this location. 



Genus ENCOPE L. Agassiz 



ENCOPE TENUIS Kew 

 Plate 36, figure 1; plate 37, figures la, Ih 



E/icope tenuis Kew. Univ. Calif. Publ. Bull. Dept. Geol., vol. 8, 1913, 



pp. 47-48, pi. 1, fig. 1; pi. 2, fig. 1. 

 Encope tenuis. Clark and Twitchell, U. S. Geol. Surv. Mon., vol. 54, 1915, 



pp. Ill, 208. 



Cotypes.—Nos. 10050 and 10051 Univ. Calif. Coll. Invert. Pal. 



Size large. Average measurements : anteroposterior diameter 102.5 

 mm., transverse diameter 100.5 mm., greatest thickness 11.5 mm. Test 

 broad, transverse diameter sometimes greater than the anteroposterior 

 diameter. Greatest width posterior to the center. Outline irregularly 

 subcircular. Test thin, with sharply angular margin. Summit pos- 

 terior to apical system, and immediately anterior to interambulacral 

 lunule or foramen. Area immediately surrounding the lunule some- 

 wliat tumid. Ambulacral notches broad, deep, contracting slightly 

 near the margin of the test and tending to close. Both interambu- 

 lacral lunule and ambulacral notches varying somewhat in size. Apical 

 system central. Petals rather narrow, nearly closed, and reaching 

 about two-thirds the distance to the margin. The two lateral petals 

 of the trivium broader, and averaging nine per cent shorter than the 

 others. Interporiferous areas somewhat lenticular, and at widest part 

 about two-thirds the width of each poriferous area. Actinal side 

 flat ; marked by deep ambulacral furrows, which branch immediately 

 from the peristome and a second time a short distance from the outer 



