  We present 15 - 20 micron long-slit spectra, from the Infrared Spectrograph
(IRS) on Spitzer, of NGC 7023. We observe recently-discovered interstellar
emission features, at 15.9, 16.4, 17.0, 17.4, 17.8, and 18.9 microns,
throughout the reflection nebula. The 16.4 micron emission feature peaks near
the photodissociation front northwest of the star, as do the aromatic emission
features (AEFs) at 3.3, 6.2 and 11.3 microns. The 16.4 micron emission feature
is thus likely related to the AEFs and radiates by non-equilibrium emission.
The new 18.9 micron emission feature, by contrast, decreases monotonically with
stellar distance. We consider candidate species for the 18.9 micron feature,
including polycyclic aromatic hydrocarbons, fullerenes, and diamonds. We
describe future laboratory and observational research needed to identify the
18.9 micron feature carrier.
