82 THE NAUTILUS. 



Notes. The angular posterior extremity gives it a distinctive 

 shape. It is named in honor of R. W. Wilcox, Delta, Colorado. 



Type. Museum, Stanford University, California. 



Locality, This specimen was found in Briones reef sandstones 

 on the north limb of the Haywards Pass syncline. It is also 

 found on the anticline northwest of Dublin, California. It is 

 also found on the Tesla Quadrangle in the clays at the mouth 

 of the small gulch joining Arroyo Seco from south, one-half 

 mile above 963 Mark, Livermore, California. 



Horizon. Briones, Middle Miocene. 



PECTEN TOLMANT, n. s. Hall and Ambrose. 



Description. Both valves convex, left more convex of two, 

 inequilateral, base regularly rounded ; margins smooth. Right 

 valve with 16 to 18 prominent rounded ribs, separated by 

 rounded interspaces, narrower than the ribs; ribs on left valve 

 more prominent and irregularly spaced; surface sculptured by 

 numerous, fine, imbricating, regular lines of growth; hinge line 

 less than one-half length of disk; ears subequal; anterior ear of 

 other specimens show 5 or 6 sharp radial lines emanating from 

 beak, crossed by fine, faint, concentric lines; sculpture of pos- 

 terior ear less distinct but truncated at right angles. 



Dimensions. Alt. 67 mm.; long. 71 mm.; diameter 9 mm.; 

 umbonal angle 130. 



Notes. This species resembles an enlarged P. andersoni but 

 is undoubtedly a new form. This form is much larger than 

 P. andersoni, the hinge (proportional to size) much shorter, and 

 the umbonal angle much larger. 



It is possible this form is a descendant of P. andersoni, of 

 Monterey times. The young are very similar to P. andersoni, 

 and it is not certain that the forms classified as P. andersoni in 

 the Briones are not the young of P. tolmani. Named in honor 

 of Prof. Cyrus Fisher Tolman, Jr. 



Type. Museum, Stanford University, Calif. 



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

 Hamilton Quadrangles. 



Horizon. Brionet, Middle Miocene ; probably Monterey, 

 Lower Miocene. 



