74 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 30 Ser. 



and incurved; surface marked with fine, regular, concentric lines; radiating 

 ridges, usually six in number, crossing the posterior surface, the last and 

 heaviest one followed by a groove extending from the beak to the margin; 

 hinge not distinct. 



Length of shell, 2.5 cm. or more; height, 2 cm.; thickness, 1.6 cm. 



Occurrence. — The species is known from five or six 

 specimens obtained by Dr. Fairbanks from the Santiago 

 and the Silverado canyons of the Santa Ana range in 

 Orange County, CaHfornia. It was associated with Pcc- 

 ttmctilus -pacijictis, Schlanbachia gahhi, and other species 

 known only in the Lower Chico. The same, or a very 

 similar species, is reported by Dr. Smith from the Lower 

 Chico of the San Fernando Mountains, Los Angeles 

 County, California. 



6. Pectunculus pacificus, sp. nov. 

 Plate VII, Fig. 159. 



cf. Pectunculus subplanatus Stol., Pal. Ind., Vol. Ill, p. 347, Pis. XVII 

 and XLIX. 

 Shell subcircular, compressed; beaks central, low, sometimes a little prom- 

 inent; surface nearly smooth, yet marked with fine radiating strite and a few 

 faint lines of growth; thickness of shell two-thirds the vertical diameter; 

 hinge-margin angularly truncated in some specimens, both anteriorly and 

 posteriorly; diameter generally 1.5 to 3 cm. 



Occurrence. — The type of this species was obtained by 

 H. W. Fairbanks from the Santiago Canyon of Orange 

 County, California, where it is associated with Schlccnbachia 

 gabbi, Baculites, fairbanksi, and other species that are 

 known only from the lower portion of the Chico. It occurs 

 also in the lower Chico beds of Southern Oregon, at the 

 Forty-nine Mine, and the Smith ranch. 



The type of this species is the property of Dr. H. W. 

 Fairbanks, Berkeley, California. 



7. Mactra gabbiana, sp. nov. 

 Plate VII, Fig. 156. 



Shell moderate in size, somewhat resembling M. ashburneri Gabb, but 

 generally with a heavier shell, and more strongly grooved concentrically; 

 umbonal angle strongly marked, especially near the base; anterior surface 

 flattened but not excavated. 



