132 University of California Publications in Geology [VOL. 8 



anterior dorsal margin very slightly convex; anterior end nearly 

 straight; ventral margin rounded; sculpture consists of raised sharp 

 incremental lines with interspaces about three times their width. 



Dimensions. Length, 10 mm. ; height, 10 mm. ; convexity, 1.5 mm. 



Occurrence. University of California Locality 784 near Lower 

 Lake. 



The quadrate shape of this species is quite sufficient to distinguish 

 it from other members of the genus. 



PHACOIDES MUIBENSIS, n. sp. 

 Plate 10, figures lla, 116 



Shell small, suborbicular, convex; beaks nearly central; in some 

 specimens slightly posterior to the center. Lunule narrow, small ; 

 escutcheon long, narrow ; posterior dorsal margin nearly straight ; 

 anterior dorsal margin slightly excavated under the beaks; anterior 

 and posterior extremities subtruncate; ventral margin broadly 

 rounded. Surface is marked by strong concentric growth lines and 

 by a very faint, narrow, posterior furrow which is absent in young 

 specimens. 



This species differs from Phacoides turneri (Stanton) in the trun- 

 cation of the extremities, in the slightly posterior position of the beak 

 and in the lesser prominence of the posterior furrow. 



Dimensions. Height, 14.5 mm.; length, 15.5 mm; convexity, 

 3.5 mm. 



Occurrence. University of California Locality 243. 



Named for its occurrence near Muir Station. 



PHACOIDES DIABOLI, n. sp. 



Plate 10, figure 7 



Shell thin, equivalve, suborbicular, nearly equilateral ; beaks promi- 

 nent, prosogyrate, central; valves convex; lunule narrow and extend- 

 ing half the length of the straight horizontal anterior dorsal margin ; 

 escutcheon narrow, two-thirds the length of the straight sloping pos- 

 terior dorsal margin and set off in each valve by a high, sharp ridge 

 from rest of shell. A rounded ridge extends from the beaks to the 

 middle of the posterior end; the portion of shell between the umbonal 

 ridge and the ridge bordering the escutcheon is slightly concave; 

 sculpture consists of sharp concentric lamellae with interspaces about 

 three times their width. 



