  We report new interferometric angular diameter observations of 41 carbon
stars observed with the Palomar Testbed Interferometer (PTI). Two of these
stars are CH carbon stars and represent the first such measurements for this
subtype. Of these, 39 have Yamashita (1972,1975) spectral classes and are of
sufficiently high quality that we may determine the dependence of effective
temperature on spectral type. We find that there is a tendency for the
effective temperature to increase with increasing temperature index by ~120K
per step, starting at T_EFF ~= 2500K for C3,y, although there is a large amount
of scatter about this relationship. Overall, the median effective temperature
for the carbon star sample is found to be 2800 +- 270K, and the median linear
radius is 360 +- 100 R_SUN. We also find agreement on average within 15K with
the T_EFF determinations of Bergeat (2001,2002a,b), and a refinement of carbon
star angular size prediction based on V & K magnitudes is presented that is
good to an rms of 12%. A subsample of our stars have sufficient {u,v} coverage
to permit non-spherical modeling of their photospheres, and a general tendency
for detection of statistically significant departures from sphericity with
increasing signal-to-noise of the interferometric data is seen. The
implications of most - and potentially all - carbon stars being non-spherical
is considered in the context of surface inhomogeneities and a rotation-mass
loss connection.
