  We present an abundance analysis for the extremely metal poor star
HE1424-0241 based on high dispersion spectra from HIRES at Keck. This star is a
giant on the lower red giant branch with [Fe/H] ~ -4.0 dex. Relative to Fe,
HE1424-0241 has normal Mg, but it shows a very large deficiency of Si, with
epsilon(Si)/epsilon(Fe) ~ 1/10 and epsilon(Si)/epsilon(Mg) ~ 1/25 that of all
previously known extremely metal poor giants or dwarfs. It also has a
moderately large deficiency of Ca and a smaller deficit of Ti, combined with
enhanced Mn and Co and normal or low C. We suggest that in HE1424-0241 we see
the effect of a very small number of contributing supernovae, and that the SNII
contributing to the chemical inventory of HE1424-0241 were biased in progenitor
mass or in explosion characteristics so as to reproduce its abnormal extremely
low Si/Mg ratio. HE1424-0241 shows a deficiency of the explosive alpha-burning
elements Si, Ca and Ti coupled with a ratio [Mg/Fe] normal for EMP stars; Mg is
produced via hydrostatic alpha-burning. The latest models of nucleosynthesis in
SNII fail to reproduce the abundance ratios seen in HE1424-0241 for any
combination of the parameter space of core-collapse explosions they explore.
