Erratum: ``A Distant Extended Spiral Arm in the Fourth Quadrant of the Milky Way'' (ApJ, 607, L127 [2004])

The model used to create the synthetic longitude-velocity (l-v) diagram displayed in Figure 3b of the original Letter contains an error and does not represent the spiral model shown in Figure 3a. The model used to produce the l-v diagram in Figure 3b uses spiral arms that are 5π/8 radians out of phase with the arms shown in the left panel of the same figure. In all other respects, the models are the same. Here we present a revised figure using the correct model for both panels. The difference in models most strongly effects the inner Galaxy and is less noticeable in the outer Galaxy at the position of the proposed arm. The correct model was used for interpretation of the data and provides a better fit to the outer spiral feature. None of the conclusions of our Letter were affected by this error.