The fine-scale spectral structure in this order is dominant until T0 composite type (Figure 5) when the spectrum becomes remarkably smooth. Here again the high resolution data reveal a striking effect, this time at the transition from L to T dwarfs. New spectral structure develops in this order between types T0 at T4.5 (Figure 6) but, as was the case for order 58, the pattern is different, indicating different atmospheric conditions.

The weak Na I line at 1.2683 $\mu$m detected in order 60 in the M6 object (Figure 1) is already absent in the M9 object (Figure 2). Otherwise, the behavior of the fine-scale structure follows a pattern similar to order 59 becoming remarkably weak at T0 (Figure 5) and leading to a smoother appearance for these spectra near the L-T transition.

Order 61 contains one of the pairs of strong K I doublets located at 1.2436 and 1.2525 $\mu$m. These lines deepen and widen slightly from M6 to M9, and then become increasingly broader and shallower from L0 to T4.5. NIRSPEC spectral order 61 also has many fine-scale features attributable to molecular transitions. Two features, one at 1.24637 and the other at 1.24825 $\mu$m have been identified previously with 