80 THE NAUTILUS. 



Notes. This form is easily recognized by its shape and pos- 

 terior truncation. Harold Hannibal has collected this form on 

 Vancouver Island in the Sooke Formation (Oligocene). The 

 writers had the opportunity of comparing the material with a 

 specimen collected by Mr. Hannibal. It showed a strong hinge, 

 a large resiliary pit, rather deep, and a thick shell, with con- 

 centric striation. 



Type. Museum, Stanford University, Calif. 



Localities. Monterey Sandstone, P. 282, on the Pleasanton 

 Quadrangle, in Alameda Creek, 1^ miles south of Mouth of 

 Welch Creek, and one-fifth mile south of Calaveras Fault, 

 Sunol, Calif. 



Horizon. Monterey Sandstone, Lower Miocene. 



Mactra beali, n. s. Hall and Ambrose. 



Description. Left valve. Shell trigonal, thin, slightly ventri- 

 cose, inequilateral ; umboes prominent ; beaks not prominent, 

 situated slightly posterior to middle of shell ; anterior margin 

 slightly curved upward, running to anterior extremity where it 

 is sharply rounded ; posterior margin practically straight, run- 

 ning to posterior extremity where it is angularly truncated ; 

 basal margin regularly curved ; posterior and anterior margin 

 make an angle of 105° at the beak ; surface smooth. 



Dimensions. Long. 44 mm. ; lat. 34 mm. ; diameter 9 mm. 



Notes. It is very similar to an unnamed form found by 

 Harold Hannibal in the Sooke formation (Oligocene) of the 

 North Pacific coast. Named in honor of C. H. Beal, Stanford 

 University, Calif. 

 'Type. Museum, Stanford University, Calif. 



Locality. Monterey Sandstones of Pleasanton Quadrangle. 

 This particular valve came from locality P. 227. 



Horizon. Monterey Sandstone, Lower Miocene. 



Briones — Middle Miocene. 

 OsTREA TITAN Courad. VAR. PERRiNi, n. var. Hall and 

 Ambrose. 

 Description. Lower valve. Shell irregularly elliptical, con- 

 tracted at beak ; beak curved toward right when viewed from 



