454 University of California Publications in Geology IT 1 



PECTEN (PALLIUM) HOLWAYI, n. sp. 

 Plate 47, figure 5 



Shell large, equilateral; posterior, anterior, and ventral margins 

 strongly depressed; surface of shell with a marked step-like depres- 

 sion, indicating a former depressed ventral margin, situated not quite 

 one third the distance from the ventral edge to the beak. Surface 

 sculptured by three heavy rounding ribs; these ribs are very promi- 

 nent between the step-like depression and the central depressed mar- 

 gin, but very faint and almost disappearing between the step and the 

 beak. Surface also sculptured by fine, regular, radial striae or riblets, 

 which cover both the interspaces and the ribs, and by fine imbricate 

 concentric lines. Shell feebly lirate internally, the lirations being most 

 prominent on the depressed area along the ventral edge. Adductor 

 muscle scar prominent. 



Named in honor of Professor R. S. Holway, Associate Professor 

 of Physical Geography at the University of California. 



Dimensions. — Height of shell, 85 mm. ; length of shell, 90 mm. ; 

 greatest diameter of valve, about 24 mm. 



Occurrence. — In Pecten beds of the Upper San Pablo group on 

 San Pablo Bay to the south of the town of Rodeo, University of Cali- 

 fornia locality 1632. 



PECTEN (PATINOPECTEN) WEAVERI, n. sp. 

 Plate 45, figures 1 and 2 

 Shell discoidal, broader than high, equilateral, nearly equivalved; 

 apical angle about 90° ; dorsal edges gently concave ; hinge line about 

 half the length of the shell. Right valve sculptured by about four- 

 teen low, broad-topped, squarish ribs, the interspaces between which 

 are flat-bottomed and about as wide as the tops of the ribs. Surface 

 concentrically sculptured by rather coarse, somewhat irregular incre- 

 mental lines. Anterior ear slightly longer than posterior, deeply 

 notched, sculptured by three medium coarse, radiating ribs. Posterior 

 ear marked by two or three faint radiating riblets. Left valve sculp- 

 tured by fourteen fairly prominent, rounded, radiating ribs with 

 interspaces about equal to the width of the ribs ; the ribs next to the 

 dorsal edges are not so prominent as the others. Surface also covered 

 by fine, sharp, incremental lines. Anterior and posterior ears each 

 marked by three medium fine, radiating riblets ; anterior edge of an- 

 terior ear slightly notched. 



