  The velocities and equivalent widths (EWs) of a set of absorption features
are measured for a sample of 28 well-observed Type Ia supernovae (SN Ia)
covering a wide range of properties. The values of these quantities at maximum
are obtained through interpolation/extrapolation and plotted against the
decline rate, and so are various line ratios. The SNe are divided according to
their velocity evolution into three classes defined in a previous work of
Benetti et al.: low velocity gradient (LVG), high velocity gradient (HVG) and
FAINT. It is found that all the LVG SNe have approximately uniform velocities
at B maximum, while the FAINT SNe have values that decrease with increasing
Delta m_15(B), and the HVG SNe have a large spread. The EWs of the Fe-dominated
features are approximately constant in all SNe, while those of Intermediate
mass element (IME) lines have larger values for intermediate decliners and
smaller values for brighter and FAINT SNe. The HVG SNe have stronger Si II
6355-A lines, with no correlation with Delta m_15(B). It is also shown that the
Si II 5972 A EW and three EW ratios, including one analogous to the R(Si II)
ratio introduced by Nugent et al., are good spectroscopic indicators of
luminosity. The data suggest that all LVG SNe have approximately constant
kinetic energy, since burning to IME extends to similar velocities. The FAINT
SNe may have somewhat lower energies. The large velocities and EWs of the IME
lines of HVG SNe appear correlated with each other, but are not correlated with
the presence of high-velocity features in the Ca II infrared triplet in the
earliest spectra for the SNe for which such data exist.
