What does callithrix mean in Latin?

callithrix, a noun, means “waterwort (Asplenium trichomanes); an Ethiopian monkey or some such animal”.

What is the genitive of callithrix?

The genitive singular is callithrichis. callithrix is feminine, third declension.

In classical Latin, [ˈkal.lɪ.tʰrɪks]; in ecclesiastical (church) Latin, [ˈkal.li.triks].

noun · femininethird declension

callithrix f (genitive callithrichis or callithrichos or callitrichos or callithricis or callitrichis)

Classical[ˈkal.lɪ.tʰrɪks]Ecclesiastical[ˈkal.li.triks]

declension
form	singular	plural
nominative	callithrix	callithrichēs
genitive	callithrichis callithrichos, callitrichos, callithricis, callitrichis	callithrichum
dative	callithrichī	callithrichibus
accusative	callithrichem	callithrichēs
ablative	callithriche	callithrichibus
vocative	callithrix	callithrichēs

callithrix, trĭchos, f., = καλλίθριξ (fair-haired).

I. A plant used for coloring the hair, also called trichomanes, Plin. 26, 15, 90, § 160; 26, 14, 87, § 147; 25, 11, 86, § 135.—

II. Plur.: callitrĭches, um, a kind of ape or monkey in Ethiopia; acc. to Lichtenstein, Simia faunus, Linn.; Plin. 8, 54, 80, § 216.

Borrowed from Ancient Greek κᾰλλῐ́θρῐξ (kăllĭ́thrĭx).