CONTENTS 



Preface 1 



Introduction 3 



Nomenclature 8 



List of specific names used for west American mytilids 9 



The "Mytilus"-group 14 



Systematical part 16 



Key to genera of mytilids based on west American species . . . . 16 



Genus Alytilus Linne 1758 18 



My tilus edulis Linne 1758 19 



Mytilus calif ornianus Conrad 1S37 22 



Genus Crenomytilus nov 23 



Genus Semimytilus nov 25 



Semimytilus algosus (Gould) 1850 25 



Genus P^rrafl Retzius 1788 29 



Perna perna (Linne) 1758 30 



Genus Choromytilus Soot-Ryen 1952 30 



Choromytilus chorus (Molina) 1782 31 



Choromytilus palliopunctatus (Carpenter) 1855 31 



Genus Aulacomya Morch 1853 32 



Aulacomya ater (Molina) 1782 Z3 



Genus Ischadium Jukes-Browne 1905 34 



Ischadium recurvus (Rafinesque) 1820 36 



Genus Hormomya Morch 1853 36 



H ormomy a adamsiana (Dunker) 1856 37 



Hormomya granulata (Hanley) 1843 40 



Genus Septifer Recluz 1848 40 



Septifer bifurcatus (Conrad) 1837 41 



Septifer zeteki Hertlein and Strong 1946 42 



Genus Brachidontes Swainson 1840 43 



Brachidontes multiformis (Carpenter) 1855 44 



Brachidontes purpuratus (Lamarck) 1819 45 



