OS. [ns] became [ss]; [-ns-] > [-ss-]

OS. medial [s] assimilated to following nasal; [-{sm|sn}-] > [-{mm|nn}-]

In the (Old) Noldorin of the 1930s, it seems that primitive [s] in combination with a nasals [m] or [n] developed into [mm] or [nn]. There are several examples in the Etymologies:

OS. final [e] became [a] after single [s] and [st]; [-se|-ste|-sse] > [-sa|-sta|-sse]

[Note: This sound change probably took place before the previous one (Part 32) but I didn't notice things were out of order and I don't want to alter the previous post. I will fix the ordering in Eldamo.]

OS. syllabic initial [s] became [es]; [ṣ-] > [es-]

OS. voiceless stops became spirants after initial [s]; [s{ptk}-] > [s{ɸθx}-]

OS. initial [s] unvoiced following consonants; [s{jwmnrl}-] > [{j̊w̥m̥n̥l̥r̥}-]

In the Primitive Eldarin of the 1930s to 1970s, many initial consonants could have an s-prefix (PE18/43, 93). For s-prefixed voiced consonants, the resulting combinations [sr-, sl-, sj-, sw-, sm-, sn-] produced corresponding voiceless consonants in (Old) Sindarin: [r̥-, l̥-, j̊-, w̥-, m̥-, n̥-].

OS. aspirates became voiceless spirants; [{ptk}ʰ|{ptk}{ptk}ʰ] > [{ɸθx}|{ɸθx}{ɸθx}]

OS. voiceless stops aspirated after consonants except [s]; [{ptkmnŋlr}{ptk}] > [{ptkmnŋlr}{ptk}ʰ]

In both Old Sindarin and Old Noldorin, voiceless stops [p, t, k] developed into spirants medially after nearly every other primitive consonant, in particular: all liquids [r, l], all nasals [m, n, ŋ], all aspirates [pʰ, tʰ, kʰ] and all other voiced and voiceless stops [b, d, g, p, t, k], that is essentially everything but [s]. In the last two cases, the both stops in the pair both became spirants, with various later vocalic effects (see below).

OS. [oi], [ǭi] became [ui], [oi]; [oi|ǭi] > [ui|oi]