. Bulletin of the British Museum (Natural History). PEBASIAN MOITUSCAN FAUNAS 291. dorsal septum from overlying resilifer; resilifer lanceolate, lying almost in plane of commissure and subparallel to hinge, bordered dorsally by elongate process which functions as posterolateral tooth; mantle cavity rather small, with pallial line some distance from commissure; pallial sinus very shallow, normally only a truncation of the pallial line in front of posterior adductor scar; anterior and posterior pedal or byssal muscle scars situated at dorsal margins of anterior and posterior adductor s
. Bulletin of the British Museum (Natural History). PEBASIAN MOITUSCAN FAUNAS 291. dorsal septum from overlying resilifer; resilifer lanceolate, lying almost in plane of commissure and subparallel to hinge, bordered dorsally by elongate process which functions as posterolateral tooth; mantle cavity rather small, with pallial line some distance from commissure; pallial sinus very shallow, normally only a truncation of the pallial line in front of posterior adductor scar; anterior and posterior pedal or byssal muscle scars situated at dorsal margins of anterior and posterior adductor scars respectively; other scars situated either just above the first anterior pedal (or byssal) or on anterovcntral surface of hinge plate and also under hinge plate. Shell structure, outer layer crossed lamellar; inner layer within pallial line, complex crossed lamellar. Other species assigned. Pachydon tenuis Gabb, 1869 ( = Pachydon ovata Conrad, 18716, = Anisothyris hauxwelli Woodward, 1871, unjustified replacement name for P. tenua Gabb); Tellina amazonensis Gabb, 1869; Pachydon carinatus Conrad, 18716; Pachydon erectus Conrad, 18716 (= Pachydon alta Conrad, 18716, = Corbula canamaensis Etheridge, 1879); Anisothyris erecta elongata Bocttger, 1878; Pachydon cuneatus Conrad, 18716 (= Anisothyris tumida Etheridge, 1879); Corbula {Anisothyris?) ledaeformis Dall, 1872; Corbula hettneri Anderson, 1928; Corbula cebada Anderson, 1928 ( = Corbula abundans Pilsbry & Olsson, 1935, = Corbula rnagda- lensis Pilsbry & Olsson, 1935); Anisothyris iquitensis dc Grevc, 1938; Pachydon trigonalis sp. nov. (p. 309); Pachydon ovalis sp. nov. (p. 305). Fig. 357 Neogene distribution of the extinct genus Pachydon. Key as for Fig. 6 (p. 177) with additions: 8, Venezuela (Rutsch 1951); 9, Peruvian localities of Bassler (Willard 1966); 10, Pachitea River as Corbula arcana (Pilsbry 1944); 11, Porto Peter, Brazil as Anisothyris acreana (Maury 1937); 12,Taterenda Formation, Bolivia, as Tellina sp.
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