  We present an observational study of the Type IIn supernovae (SNe IIn) 2005ip
and 2006jd. Broad-band UV, optical and near-IR photometry, and
visual-wavelength spectroscopy of SN 2005ip complement and extend upon
published observations to 6.5 years past discovery. Our observations of SN
2006jd extend from UV to mid-infrared wavelengths, and like SN 2005ip, are
compared to reported X-ray measurements to understand the nature of the
progenitor. Both objects display a number of similarities with the 1988Z-like
subclass of SN IIn including: (i) remarkably similar early- and late-phase
optical spectra, (ii) a variety of high ionization coronal lines, (iii)
long-duration optical and near-IR emission and, (iv) evidence of cold and warm
dust components. However, diversity is apparent including an unprecedented
late-time r-band excess in SN 2006jd.The observed differences are attributed to
differences between the mass-loss history of the progenitor stars. We conclude
that the progenitor of SN 2006jd likely experienced a significant mass-loss
event during its pre-SN evolution akin to the great 19th century eruption of
\eta Carinae. Contrarily, as advocated by Smith et al. (2009), we find the
circumstellar environment of SN 2005ip to be more consistent with a clumpy wind
progenitor.
