  There is a puzzle in the $\Lambda_c^+$ family, i.e., one member with
$J^P=3/2^+$ is missing in a $L=2$ multiplet which the heavy quark effective
theory predicts, and $J^P$'s of $\Lambda_c(2765)^+$ and $\Lambda_c(2940)^+$ are
unknown. Using a light diquark picture to calculate baryon masses, we study
possible assignments of two $\Lambda_c$'s with unknown $J^P$ and the missing
$\Lambda_c^+$ with $3/2^+$ for $L=2$, and we find the most probable possibility
that the peak corresponding to $\Lambda_c(2880)^+$ actually includes a missing
member with spin $3/2^+$ for $L=2$ and that quantum numbers of
$\Lambda_c(2765)^+$ and $\Lambda_c(2940)^+$ are $2S(1/2^+)$ and $2P(1/2^-)$,
respectively.
