Luminosity versus mass for all clumps (black “+” signs) observed at Arecibo, estimated using the distances listed in Table 1. Sources where a methanol or OH maser has been detected are shown in red and blue, respectively; sources with both masers are shown in green (both newly detected and previously known masers are shown). The dashed lines are loci at constant T = 10, 20, 30, and 40 K. Roughly orthogonal to these are loci (dotted lines) of constant 250 μm flux density, ranging from 0.1 to 500 Jy (assuming a modified blackbody spectral energy distribution with β = 1.5 and a fixed, “typical” distance of ~6 kpc).