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UM 670 (Q0114-089), a reasonably bright (V =17.4), high redshift (z$_{em}$=3.16) quasar whose spectrum is not cut off in the visible by any Lyman limit system, was observed with the G160L configuration of the Faint Object Spectrograph (FOS) on board the Hubble Space Telescope between 1200 and 2250 \AA\ as part of FOS GTO programs 3268 and 4856. The spectrum is cut off at $\sim$1340 \AA, below which no light is present. If this cutoff is due to a low redshift Lyman limit system, the redshift for this system is about 0.47. No obvious Ly$\alpha$ line is present at this redshift but the spectrum is very noisy. A search in the optical for the associated Mg II doublet turned up two lines with the correct separation near the expected redshift. It is possible that this is just fortuitous since the Ly$\alpha$ forest is fairly well populated. An alternate explanation is that the break is due to intergalactic He II $\lambda$304 at high redshift, but the cutoff is about 18 \AA\ (rest) longward of the wavelength expected for this feature. A third possibility is that the break is due to some high ionization feature, possibly He II $\lambda$304, associated with the quasar. We note that another high redshift QSO, OQ 172 (Q1442+101, z$_{em}$=3.54), is cut off about 21 \AA\ (rest) longward of the wavelength expected for intergalactic He II. If this absorption is due to a Lyman limit system, then the redshift of this system is similar, about 0.62 (Lyons et al. 1995). \\
We gratefully acknowledge the support of NASA through NAS5-29293 and NAG5-1630.
