Tri-carinate: with three keels or carinae.
Trichogen: a hair-forming hypodermal cell in caterpillars, etc.
Trichoptera: hairy-winged: insects with hairy primaries with many longitudinal veins and cells, covering the broader secondaries which are usually folded lengthwise; mouth mandibulate but rudimentary: head free; thorax agglutinate: metamorphosis complete.
Trichostical bristles: in Diptera, a fan-like row, situated on the meta- pleura: conspicuous in some families.
Trichotomous: divided by threes.
Trichroism: the condition when any given part exhibits three different colors in different individuals of the same species: e.g. in Lepidoptera, the hind wings of certain Heliconids.
Tricuspidate: ending in three points: with three cusps or teeth.
Tridactyle -ous: having three toes or claws.
Trifid: cleft into three parts or ends.
Trigonal: triangular: an area bounded by a triangle.