Optical spectra of PS16dtm from +25 to +189 rest-frame days relative to the beginning of the rise. The +25-day spectrum was obtained by Terreran et al. (2016). See Table 3 for details on the spectroscopic observations. The spectra show very little evolution over ∼170 days, maintaining a blue continuum with multicomponent Balmer and Fe II emission lines (marked by orange lines). We also show two epochs of spectra of CSS100217, another luminous transient coincident with the nucleus of an NLS1 galaxy (Drake et al. 2011).