Brachidontes playasensis (FilshTy and Olsson) 1935 . ... 46 



Brachidontes puntarenensis (Pilsbry and Lowe) 1932. ... 46 



Brachidontes houstonius Bartsch and Rehder 1939 47 



Genus Mytella nov 47 



Mytellajalcata {Ox\yigny) \%A(i 50 



Mytella speciosa {Rttwt) 1857 52 



Mytella guyanensis (Lamarck) 1819 5Z 



Genus A rcuatula l^s.my \9\9 55 



Arcuatula demissa (Dillwyn) 1817 56 



Genus Modiolus Lamarck 1799 56 



Modiolus capax (Conrad) 1837 60 



Modiolus fornicat US (Carpenter) 1865 62 



Modiolus rectus (Conrad) 1837 63 



Modiolus eiseni Strong and Hertlein 1937 64 



Modiolus neglectus n. sp 64 



Modiolus sacculifer (Berry) 1953 65 



Modiolus modiolus (Linne) 1758 66 



Modiolus americaniis (Leach) 1815 67 



Genus ^/;2j;^fi?c/z//« Megerle von Miihlfeld 1811 68 



Amygdalum pallidulum (Dall) 1916 . 69 



Amygdalum americanum n. sp 70 



Genus Lio^^rw^ Dall 1898 71 



Lioberus salvadoricus (Hertlein and Strong) 1946 . ... 72 



Genus Musculus Roding 1798 72 



Musculus senhousei (Benson) 1842 74 



Musculus olivaceus Dall 1916 75 



Musculus protractus Dall 1916 75 



Genus Gregariella Monterosato 1834 76 



Gregariella coarctata (Carpenter) 1856 77 



Gregariella chenui (Recluz) 1842 78 



Gregariella denticulata (Dall) 1871 79 



Genus Crenella Brown 1827 79 



Crenella divaricata (Orbigny) 1853 80 



