56. Masculine and feminine nouns with mute stems form the nominative by adding s to the stem.
A labial (p) is retained before s.
A lingual (t, d) is dropped before s.
mīles (stem mīlit-)
cūstōs (stem cūstōd-)
A palatal (c, g) unites with s to form x.
dux (for † duc-s)
rēx (for † rēg-s)
In dissyllabic stems the final syllable often shows e in the Nominative and i in the stem.
prīnceps, stem prīncip- (for -cap-)
57. Nouns of this class are declined as follows.
a. In like manner are declined—
ariēs, -etis (m.) ram
comes, -itis (m. / f.) companion
lapis, -idis (m.) stone
iūdex, -icis (m.) judge
cornīx, -īcis (f.) raven
and many other nouns.