We present central CaT , PaT , and CaT* indices for a sample of fifteen dwarf elliptical galaxies ( dEs ) .
Twelve of these have CaT* \sim 7 Å and extend the negative correlation between the CaT* index and central velocity dispersion \sigma , which was derived for bright ellipticals ( Es ) , down to 20 < \sigma < 55 km/s .
For five dEs we have independent age and metallicity estimates .
Four of these have CaT* \sim 7 Å , much higher than expected from their low metallicities ( -1.5 < [ Z/H ] < -0.5 ) .
The observed anti-correlation of CaT* as a function of \sigma or Z is in flagrant disagreement with theory .
We discuss some of the amendments that have been proposed to bring the theoretical predictions into agreement with the observed CaT*-values of bright Es and how they can be extended to incorporate also the observed CaT*-values of dEs .
Moreover , 3 dEs in our sample have CaT* \sim 5 Å , as would be expected for metal-poor stellar systems .
Any theory for dE evolution will have to be able to explain the co-existence of low-CaT* and high-CaT* dEs at a given mean metallicity .
This could be the first direct evidence that the dE population is not homogeneous , and that different evolutionary paths led to morphologically and kinematically similar but chemically distinct objects .