I present new results from a continuing program to identify and characterize the low-mass stellar and substellar populations in the young cluster IC 348 ( 1-10 Myr ) .
Optical spectroscopy has revealed young objects with spectral types as late as M8.25 .
The intrinsic J - H and H - K colors of these sources are dwarf-like , whereas the R - I and I - J colors appear intermediate between the colors of dwarfs and giants .
Furthermore , the spectra from 6500 to 9500 Å are reproduced well with averages of standard dwarf and giant spectra , suggesting that such averages should be used in the classification of young late-type sources .

An H-R diagram is constructed for the low-mass population in IC 348 ( K6-M8 ) .
The presumably coeval components of the young quadruple system GG Tau ( White et al . )
and the locus of stars in IC 348 are used as empirical isochrones to test the theoretical evolutionary models .
The calculations of Burrows et al .
do not appear to be consistent with the data at these earliest stages of stellar evolution .
There is fair agreement between the data and the model isochrones of D ’ Antona & Mazzitelli , except near the hydrogen burning limit .
The agreement can not be improved by changing the conversion between spectral types and effective temperatures .
On the other hand , for the models of Baraffe et al. , an adjustment of the temperature scale to progressively warmer temperatures at later M types , intermediate between dwarfs and giants , brings all components of GG Tau onto the same model isochrone and gives the population of IC 348 a constant age and age spread as a function of mass .
When other observational constraints are considered , such as the dynamical masses of GM Aur , DM Tau , and GG Tau A , the models of Baraffe et al .
are the most consistent with observations of young systems .
With compatible temperature scales , the models of both D ’ Antona & Mazzitelli and Baraffe et al .
suggest that the hydrogen burning mass limit occurs near M6 at ages of \lesssim 10 Myr .
Thus , several likely brown dwarfs are discovered in this study of IC 348 , with masses down to \sim 20 -30 M _ { J } .