EXPLANATION OF PLATE 18 

 All figures approximately natural size. 

 Fig. 1. Pecten crassicardo biformatus, n. var. Exterior view of left valve ; 

 Univ. Calif. Coll. Invert. Palae. type specimen no. 11308; locality 3029; Santa 

 Margarita. 



Fig. la. Pecten crassicardo biformatus, n. var. View of left valve showing 

 narrow ribs. 



Fig. lb. Pecten crassicardo biformatus, n. var. Eight valve of same speci- 

 men as figure la. 



[322] 



