Geological Papers. 103 



ceatric striae. A raised area, transversely sculptured by continua- 

 tions of the concentric strise, passes posteriorly on either side of the 

 escutcheon from the umbones to the posterior margin of the shell. 

 Both the anterior and posterior teeth are bent, the angle of eacl 

 being directed toward the beak. Margin entire ; cavity of shell 

 rather deep. On the interior of the posterior end is an elongated, 

 somewhat arrow-head shaped, raised process. The escutcheon is 

 smooth. 



Dimensions: Length, 6 mm.; height, 3 mm.; umbo to posterior 

 end, 4 mm.; to anterior end, 2 mm. 



Pecten (Chlamys) jordani (Arnold). Figure 4a. 



Arnold's description : "^ "Shell of medium size, shape of P. 

 hericeus, inequivalve, rather thin ; right valve with twenty-five to 

 thirty angular, smooth-topped, imbricated ribs, which become di- 

 chotomous after reaching a length of about 30 mm.; interspaces 

 deeply channeled and narrower than the ribs ; anterior ear imper- 

 fectly radially ribbed with six ridges, and showing elevated, con- 

 centric, incremental lines; posterior ear nearly obsolete, showing 

 four ribs ; byssal notch not deep ; left valve shows twenty-five to 

 thirty narrow, convex ribs, showing imbrications only slightly ; in- 

 terspaces as large as ribs; after a diameter of about 30 mm. has 

 been reached by the shell, small riblets appear in the widening in- 

 terspaces; anterior ear shows five narrow imbricated ridges, with 

 wide interspaces; both valves show a tendency to contract sud- 

 denly at the basal margin upon nearing a completion of growth ; 

 surface of both valves covered with a minute, lattice-like sculpture 

 which is generally worn off on exposed portions of the shell. 



"Allied to P. opuyitia (DalL), but having fewer ribs on disk and 

 ear, and having dichotomous ribs after reaching a diameter of 

 35 mm. Distinguished from P. hericeus and P. hastatios by not 

 having fasciculated nor spinose ribs." 



Pleistocene: San Pedro and Santa Barbara, Cal. (Arnold). 



Pliocene : San Pedro and Santa Barbara, Deadman island, and 

 Packard's Hill, Cal. (Arnold). 



Dimensions: Length, 42 mm. ; alt., 48 mm. 



Pecten rubidos (Hds.) (?) Figures 5a, 56, and 5c. 



Shell of medium size; right valve with twenty-five to thirty 

 broad, smooth-topped, very prominent imbricated ribs which be- 

 come dichotomous after reaching a length of 45 mm. and also just 

 before reaching the ventral margin ; interspaces deeply channeled 



6. Loc. Git., p. III. 



