on the core (C), offset 1 N, and offset 15 N. The core has a stronger contribution from stellar continuum, but otherwise the spectra are similar. We therefore detect no spectral differences between the N extension and the nebula near the core.

### M 4–18

This young, low-excitation PN was recently imaged with HST by Dayal et al. (1997) and shows a toroidal shell surrounding the central star. There is strong mid-IR emission from warm ($\sim$ 200 K) dust that has a similar morphology but the position angle of the dust emission maxima is orthogonal to those shown in H$\alpha$ emission. The spectrum of the core of this PN shown in Figure 14 has strong stellar continuum, as well as and line emission. The slit was positioned N-S across the compact ring of the PN, so the ionized regions of the nebula are included in this spectrum.

 - line and 2 emission
----------------------

The emission lines present in the spectra of this PNe group contain those mentioned in the previous section plus lines of molecular hydrogen. The 2 lines are strongest in the K band, although in some objects there are lines visible in the H and J bands as 