  A charged particle (electron or hole) confined in nanorod of strongly prolate
ellipsoidal shape is considered. The effective-mass Schr\"odinger equation is
solved in prolate spheroidal coordinates and asymptotically exact expressions
for the energy spectrum and wavefunctions are derived. It is shown that the
treatment of the confinement energies is incorrect if the actual shape of
ellipsoidal nanorod is not taken into account. In particular, developed earlier
the approach based on the consideration of the problem in cylindrical
coordinates with the use of parabolic potential leads to the incorrect
expression for the energy spectrum. Rule of correlation between the states
corresponding to spherical quantum dot and nanorod of strongly prolate
ellipsoidal shape is suggested and an appropriate energy correlation diagram is
constructed. The correlation diagram is in complete qualitative and
quantitative agreement with the energy diagram obtained by numerical solution
of the Schr\"odinger equation in spheroidal coordinates.
