156 ALLAN' HANCOCK PACIFIC EXPEDITION'S \0L. 20 



PLATE 1 



Fig. 1. Mytilus tJulis Linne 175S. San Pedro. Common low form. 

 Length: 38.6 mm. 



Fig. 2. Mytilus eJulis Linne 1758. Mission Bay, San Diego. High 

 form (Jii{/i-risis C'oe). Length: 62 mm. 



Fig. 3. Mytilus californianus Conrad 1837. San Pedro. Narrow 

 worn form from surf zone. Length: 62.2 mm. 



Fig. 4. Mytilus californianus Conrad 1837. San Pedro. High hay 

 form. Length : 45 mm. 



Fig. 5. Choromytilus palliopuncialus (Carpenter) 1855. Salina 

 Cruz, Oaxaca, Mexico. Length: 65 mm. 



Fig. 6. Aulacomya ater (Molina) 1782. Off Middle Chincha Is- 

 land, Peru. Length: 105 mm. 



