  The success of the Transiting Exoplanet Survey Satellite (TESS) mission has
led to the discovery of an abundance of Venus Zone (VZ) terrestrial planets
that orbit relatively bright host stars. Atmospheric observations of these
planets play a crucial role in understanding the evolutionary history of
terrestrial planets, past habitable states, and the divergence of Venus and
Earth climates. The transmission spectrum of a Venus-like exoplanet can be
difficult to distinguish from that of an Earth-like exoplanet however, which
could severely limit what can be learned from studying exoVenuses. In this work
we further investigate differences in transmission between hypothetical
exoEarths and exoVenuses, both with varying amounts of atmospheric carbon
dioxide (CO$_2$). The exoEarths and exoVenuses were modelled assuming they
orbit TRAPPIST-1 on the runaway greenhouse boundary. We simulated James Webb
Space Telescope (JWST) Near-Infrared Spectrograph (NIRSpec) PRISM transit
observations of both sets of planets between 0.6-5.2 $\mu$m, and quantified the
detectability of major absorption features in their transmission spectra. The
exoEarth spectra include several large methane (CH$_4$) features that can be
detected in as few as 6 transits. The CH$_4$ feature at 3.4 $\mu$m is the
optimal for feature for discerning an exoEarth from an exoVenus since it is
easily detectable and does not overlap with CO$_2$ features. The sulfur dioxide
(SO$_2$) feature at 4.0 $\mu$m is the best indicator of an exoVenus, but it is
detectable in atmospheres with reduced CO$_2$ abundance.
