S. occidentalis

S. occidentalis may refer to:
 * Sarcoscypha occidentalis, the stalked scarlet cup or western scarlet cup, a mushroom species
 * Sceloporus occidentalis, the Western fence lizard, a reptile species common in California
 * Senna occidentalis, a pantropical plant species
 * Simosthenurus occidentalis, the short-faced kangaroo, an extinct marsupial species
 * Sorbus occidentalis, a tree species in the genus Sorbus found in Western North America