400 CALIFORNIA ACADEMY OF SCIENCES. 



EXPLANATION OF PLATE XIX. 



Fig. I. Mactra {Spisji/a) falcata GouLD. Upper San Pedro series, San Pedro. Interior 



of left valve. Longitude 47 mm.; natural size. 176 



Fig. 2. Madra califor7iica Conrad. Upper San Pedro aeries, San Pedro. Interior of left 



valve. Longitude 39 mm. ; natural size. 174 



Fig. 3. Mactra hemphilli Dall. Upper San Pedro series, San Pedro. Interior of right 



valve. Longitude 124 mm; natural size. i75 



Fig. 4. Mactra exoleta Gray. Upper San Pedro series, San Pedro. Interior view, right 



valve. Longitude 57 mm.; natural size. I75 



Fig. 5. Mactra {Spisula) catilliformis CoNRAD. Upper San Pedro series, San Pedro. In- 

 terior of right valve. Longitude 125 mm.; natural size. 176 



