  We present an elemental-abundance analysis of an extremely metal-poor (EMP;
[Fe/H] < -3.0) star, SDSS J134338.67+484426.6, identified during the course of
the MARVELS spectroscopic pre-survey of some 20000 stars to identify suitable
candidates for exoplanet searches. This star, with an apparent magnitude V =
12.14, is the lowest metallicity star found in the pre-survey, and is one of
only ~20 known EMP stars that are this bright or brighter. Our high-resolution
spectroscopic analysis shows that this star is a subgiant with [Fe/H] = -3.42,
having "normal" carbon and no enhancement of neutron-capture abundances.
Strontium is under-abundant, [Sr/Fe] =-0.47, but the derived lower limit on
[Sr/Ba] indicates that Sr is likely enhanced relative to Ba. This star belongs
to the sparsely populated class of alpha-poor EMP stars that exhibit low ratios
of [Mg/Fe], [Si/Fe], and [Ca/Fe] compared to typical halo stars at similar
metallicity. The observed variations in radial velocity from several epochs of
(low- and high-resolution) spectroscopic follow-up indicate that SDSS
J134338.67+484426.6 is a possible long-period binary. We also discuss the
abundance trends in EMP stars for r-process elements, and compare with other
magnesium-poor stars.
