THE NAUTILUS. 81 



exterior ; right valve very ventricose ; extremely laminated, 

 giving rough plaited surface ; left valve almost flat, laminated ; 

 muscle-scars distinct ; hinge long, narrowing at beak, viewed 

 from interior curves to left ; cavity of hinge deep, coarsely 

 wrinkled, with wrinkles running up onto either side of hinge ; 

 interior of hinge ends abruptly, cutting at right angles toward 

 interior of shell, although not characteristic of all forms. 



Dimensions. Alt. 155 mm. ; long, maximum at base, 85 mm., 

 minimum near beak 56 mm. ; diameter lower valve 61 mm. 



Notes. This species greatly resembles 0. titan Conrad, the 

 main difference between the two being in the hinge. This vari- 

 ety has a long curved pointed hinge, while the 0. titan has a 

 much shorter hinge, about as wide as long. Also the summit 

 of this variety does not rise above the beak of the opposite valve. 

 All forms do not have as curved a hinge as this one figured. It 

 is generally elongate, and seldom, if ever, has the subcircular 

 shape the 0. titan often has. 



It is very abundant in the Briones, and may generally be 

 found any place in the Briones on the Tesla, Pleasanton, Mt. 

 Hamilton or San Jose Quadrangles. This particular specimen 

 is slightly smaller than the ordinary 0. titan var. perrini. 



It is named in honor of Professor James Perrin Smith. 



Type. Museum, Stanford University, Calif. 



Locality. Briones of the Tesla, Pleasanton, San Jose and 

 Mt. Hamilton Quadrangles, Calif. 



Horizon. Briones, Middle Miocene. 



Macoma wilcoxi. Hall and Ambrose. 



Description. Right valve ; shell thin, elongate, inequilateral ; 

 surface smooth ; beaks, small, low, pointed, nearly medial, 

 curved slightly toward posterior end ; anterior extremely regu- 

 larly rounded ; posterior dorsal margin straight, sloping more 

 steeply from beak than anterior dorsal margin toward extremity 

 which is angulated at a point somewhat below the horizon- 

 tal medial line of the valve ; base curved. Hinge unknown, 

 interior inaccessible. 



Dimensions. Long., 31 mm.; lat. , 18 mm.; diameter, 5 mm. 



