1' L A T E X L 1 X . 



pli()(.;enI': ['ECtens. 



[UnU'ss (ilht*r\vis(.' ^I:lU'(l all tiguri's aru api>r'ixini!itrly natural size.] 



Page. 



Fkj. 1. I'eclni (I'liKjioctiiiiuiii) (vtcowks/.s (iabb. l'. (' 123 



Exterior of rijrlit valve (anterior ear .sonicuiiut iiiiijerl'cct ); altitude loii iniii. I'linceiu-, 

 Cerros Island, off Lower California. (S. ) 



Fig. 1(1. Same specimen as fi";. 1 - 123 



Exterior of left valve (anterior ear slightly broken). (S. ) 



Fig. \b. Same specimen as li>;. 1 123 



Profile of both valves as viewed from tlie rear. 



Fig. 2. Pecteii (I'laijioiieii'min) coupiri u. i^\\. I). \. T.vpe 124 



Exterior of riijht valve (anterior ear .'<ome\vliat imperfect); altitude 35 mm. San Diego 

 formation (Pliocene), Pacific Beach, San Diego County, Cal. (M. H. ) 



Fig. 3. I'e.diii (I'laijiocUmium) roopenw. ii\\. D. .\. Cotj'pe 124 



Exterior of right valve; altitude 30 uiin. Same locality as tig. 2. ( M. P..) 



Fig. 4. J'ei-leii { I'liK/lodfiiitim) i-oojieri n. ^k D. .\. Type 124 



Exterior of left valve; altitude 27 mm. Same locality as tig. 2. (M. B. ) 

 242 



