  Ground-based and Hubble Space Telescope observations are presented for SN
1993J and SN 1998S. SN 1998S shows strong, relatively narrow circumstellar
emission lines of N III-V and C III-IV, as well as broad lines from the ejecta.
Both the broad ultraviolet and optical lines in SN 1998S indicate an expansion
velocity of ~7,000 km/s. The broad emission components of Ly-alpha and Mg II
are strongly asymmetrical after day 72 past the explosion, and differ in shape
from H-alpha. Different models based on dust extinction from dust in the ejecta
or shock region, in combination with H-alpha from a circumstellar torus, are
discussed. It is concluded, however, that the double-peaked line profiles are
more likely to arise as a result of optical depth effects in the narrow, cool,
dense shell behind the reverse shock, than in a torus-like region. The
ultraviolet lines of SN 1993J are broad, with a box-like shape, coming from the
ejecta and a cool dense shell. The shapes of the lines are well fitted with a
shell with inner velocity ~7,000 km/s and outer velocity ~10,000 km/s. For both
SN 1993J and SN 1998S a strong nitrogen enrichment is found, with N/C~12.4 in
SN 1993J and N/C~6.0 in SN 1998S. From a compilation of all supernovae with
determined CNO ratios, we discuss the implications of these observations for
the structure of the progenitors of Type II supernovae.
