Local atomic arrangements and wide tilings for two types of decagonal quasicrystals, which are formed in alloys with compositions near Al₇₀Ni₁₅Co₁₅, were studied by high-resolution electron microscopy. The decagonal quasicrystals can be interpreted as structures formed with different tilings, so-called rhombic and pentagonal ones, which are constructed with definite linkages of similar atom clusters.