450 



University of California Publications in Geology [Vol. 8 



PEGTEN (PLAGIOCTENIUM ?) CEASSIEADIATUS, n. sp. 

 Plate 47, figure 7 



Shell medium in size; fairly heavy; apical angle about 98° ; height 

 about equal to the length ; dorsal edges nearly straight. Hinge plate 

 over half the length of the shell. Right valve sculptured by sixteen 

 heavy, broadly rounded, radiating ribs, which become somewhat nar- 

 rower near the margins ; interspaces very narrow and deep. Dorsal 

 margins rather strongly depressed, the depressed area being narrow 

 and without ribs. Anterior ear longer than posterior, deeply notched 

 with anterior edge gently convex, sculptured by four fairly heavy 

 radiating ribs. Left valve unknown. 



This species appears to be quite unique. The writer has seen only 

 one specimen of the right valve. 



Dimensions. — Height 47 mm. ; length apparently about the same 

 as height. 



Occurrence. — In the lower San Pablo, associated with Astrodapsis 

 tumiclus, subsp. cierboensis, Scutella pabloensis, Chrysodonms pablo- 

 ensis, etc., University of California locality 367. 



PECTEN (PECTEN) EAYMONDT, n. sp. 

 Plate 46, figures 1 and 2; plate 47, figures 1 and 2 

 Shell rather heavy, subcircular, nearly equilateral, inequivalved ; 

 hinge line averaging slightly more than one half the length of the 

 shell ; height about equal to length. Anterior ears slightly longer than 

 posterior ears. Apical angle about 102°. Dorsal edges slightly con- 

 cave ; posterior edge longer than anterior edge. Left valve ventricose, 

 sculptured by seventeen to twenty squarish to slightly rounding, 

 heavy, radiating ribs, the interspaces averaging about the same width 

 as the ribs ; on some specimens the ribbing tends to become a little 

 finer toward the dorsal edges than on the middle of the disk. Surface 

 also covered by medium fine to coarse concentric lines of growth. 

 Anterior ear sculptured by three to five medium fine radiating ribs ; 

 anterior margin of ear slightly notched. Posterior ear with four to 

 five radiating ribs, posterior edge straight, and sloping forwards. 

 Right valve flat, sculptured by seventeen to twenty radiating flat- 

 topped ribs which are usually not as prominent as the ribs of the left 

 valve. On some of the smaller specimens the right valve is slightly 

 ventricose but never so much as the left valve. Interspaces between 



