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CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



EXPLANATION OF PLATE 11. 



Fig. la. Venericardia planicosta merriami, new subspecies, xl. This 

 form in the adult lacks the marked radial ribbing of the 

 typical V. planicosta. The type specimen which is figured is 

 an extreme case of this lack of radial ribbing. Other adult 

 individuals associated with it show obscure ribs in the um- 

 bonal region. A very characteristic form of the Siphonalia 

 sutterensis Zone. 



Fig. \b. Venericardia planicosta merriami, new subspecies, xl. This is 

 a figure of a young individual which shows about the same 

 type of ribbing as V. planicosta hornii (Gabb), its probable 

 progenitor. 



Fig. 2a. Pitaria martini, new species, xl. A side view of the type 

 specimen. 



Fig. 2b. Pitaria martini, new species, xl. Side view of a smaller speci- 

 men than the type. 



Fig. 2c. Pitaria martini, new species, xl. View showing hinge of same 

 specimen as Fig. 2h. 



Fig. 2ia. Tivela weaveri, new species, xl. Side view. 



Fig. Zb. Tivela weaveri, new species, xl. View showing hinge. 



Fig. 3c. Tivela weaveri, new species, xl. Side view of smaller speci- 

 men than the type. 



Fig. 4a. Siphonalia clarki, new species, xl. Mouth view. 



Fig. Ah. Siphonalia clarki, new species, xl. Back view. 



Fig. Sa. Cerithiopsis oregonensis, new species, x2. View showing 

 mouth. 



Fig. 5b. Cerithiopsis oregonensis, new species, x2. Back view. 



