  We present an analysis of HI, H-alpha, and oxygen abundance data for NGC
3741. This galaxy has a very extended gas disk (~8.8 times the Holmberg
radius), and a dark to luminous (i.e. stellar) mass ratio of ~149, which makes
it one of the ``darkest'' dwarf irregular galaxies known. However its ratio of
baryons (i.e. gas + stellar) mass to dark mass is typical of that in galaxies.
Our new high-resolution HI images of the galaxy show evidence for a large scale
(purely gaseous) spiral arm and central bar. Despite the gaseous spiral feature
and the on-going star formation, we find that the global gas density in NGC
3741 is significantly lower than the Toomre instability criterion. We also find
that the star formation rate is consistent with that expected from the observed
correlations between HI mass and SFR and the global Kennicutt-Schmidt law
respectively. We measure the oxygen abundance to be 12+ log(O/H)=7.66$\pm$0.10,
which is consistent with that expected from the metallicity-luminosity
relation, despite its extreme gas mass ratio. We also examine the issue of
chemical evolution of NGC 3741 in the context of closed-box model of chemical
evolution. The effective oxygen yield of NGC 3741 is consistent with recent
model estimates of closed-box yields, provided one assumes that the gas has
been efficiently mixed all the way to edge of the HI disk (i.e. >8 times the
optical radius). This seems a priori unlikely. On the other hand, using a
sample of galaxies with both interferometric HI maps and chemical abundance
measurements, we find that the effective yield is anti-correlated with the
total dynamical mass, as expected in leaky box models (slightly abridged).
