56 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Seb. 



Genus POROMYA Forbes 



Poromya gabbiana, new species 



Plate 3, figures 7a and 7b 



Shell of medium size, thin, convex, elongate, subquadrate, 

 equivalve, inequilateral; beaks turned inward; umbones incon- 

 spicuous, a little anterior to the center; extremities well 

 rounded ; anterior dorsal margin slightly convex ; posterior 

 dorsal margin concave; base straight, parallel to the dorsal 

 margin, contracted in the middle; surface sculptured with 

 numerous fine concentric lines and small, almost invisible, 

 radial striations, these crossed diagonally by low distant ridges 

 that originate on the posterior dorsal margin, making a sharp 

 convex bend toward the beaks, and then curving gradually 

 downward toward the anterior ventral margin and disappear- 

 ing on the dorsal area ; there are fifteen of these ridges on the 

 type specimen, and nearly twice that number on some of the 

 cotypes ; one cardinal tooth in each valve, the cardinal in the 

 left valve diagonally elongate ; ligament external ; muscular 

 impressions inaccessible. 



Dimensions: — Length of the type, 46 mm.; altitude, 22.5 

 mm. ; diameter of single valve, 8 mm. 



Occurrence : — Lower Miocene of San Luis Obispo County, 

 California, locality 126. 



The living members of this genus are subtropical in habitat. 

 None has been reported from the Miocene of California pre- 

 vious to this account. 



Type: — No. 109, and cotype No. 110, Cal. Acad. Sci., in 

 bed of a small creek near the center of Sec. 34, T. 28 S., R. 

 15 E., San Luis Obispo County, California. Coll., Bruce 

 Martin. 



Named in honor of Wm. Gabb. 



Genus DIPLODONTA Bronn 



Diplodonta buwaldana, new species 



Plate 3, figures la and lb 



Shell small, thick, subcircular in outline, inflated; valves 

 equal, inequilateral, slightly elevated in front of the beaks; 

 beaks prominent, elevated, turned forward, slightly anterior to 



