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 \sim 7 , 000 ~ { } km~ { } s ^ { -1 } .
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 \sim 7 , 000 ~ { } km~ { } s ^ { -1 } and outer velocity \sim 10 , 000 ~ { } km~ { } s ^ { -1 } .
For both SN 1993J and SN 1998S a strong nitrogen enrichment is found , with N/C \approx 12.4 in SN 1993J and N/C \approx 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 .