We have discovered a molecular dome-like feature towards $355^{circ} leq l leq 359^{circ}$ and $0^{circ} leq b leq 2^{circ}$. The large velocity dispersions of 50--100 km s$^{-1}$ of this feature are much larger than those in the Galactic disk and indicate that the feature is located in the Galactic center, probably within $sim1$ kpc of Sgr A$^{*}$. The distribution has a projected length of $sim600$ pc and height of $sim300$ pc from the Galactic disk and shows a large-scale monotonic velocity gradient of $sim130$ km s $^{-1}$ per $sim600$ pc. The feature is also associated with HI gas having a more continuous spatial and velocity distribution than that of $^{12}$CO. We interpret the feature as a magnetically floated loop similar to loops 1 and 2 and name it loop 3. Loop 3 is similar to loops 1 and 2 in its height and length but is different from loops 1 and 2 in that the inner part of loop 3 is filled with molecular emission. We have identified two foot points at the both ends of loop 3. HI, $^{12}$CO and $^{13}$CO datasets were used to estimate the total mass and kinetic energy of loop 3 to be $sim3.0 times 10^{6} Mo$ and $sim1.7 times 10^{52}$ ergs. The huge size, velocity dispersions and energy are consistent with the magnetic origin the Parker instability as in case of loops 1 and 2 but is difficult to be explained by multiple stellar explosions. We argue that loop 3 is in an earlier evolutionary phase than loops 1 and 2 based on the inner-filled morphology and the relative weakness of the foot points. This discovery indicates that the western part of the nuclear gas disk of $sim1$ kpc radius is dominated by the three well-developed magnetically floated loops and suggests that the dynamics of the nuclear gas disk is strongly affected by the magnetic instabilities.
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