  Space Telescope Imaging Spectrograph (STIS) and archival International
Ultraviolet Explorer (IUE) data were used to search for structure in the
ultraviolet interstellar extinction curve. Between 1250 and 3200 A, in addition
to the well-known 2175 A bump, there is only one fairly small (10%) absorption
feature at 2700 A. The feature is very broad (>400 A). It coincides extremely
well in position and shape with laboratory measurements of presolar diamond
grains found in meteorites. As this feature appears in both the new STIS and
archival IUE data, it is unlikely to be an instrumental effect. This feature
appears to be ubiquitous in the ISM as it is seen along sightlines toward
various clouds with reddenings in the range of E(B-V) = 0.35 to 1.73 mag. The
identification with diamonds remains tentative since it is based on a single,
weak feature. If the feature is due to interstellar diamonds then they require
an order of magnitude more absorption strength per gram/cm^2 than the presolar
meteoritic diamonds measured in the lab.
