TRIDACTYLE. — Three-fingered, or composed of three movable parts attached to a common base.

TRILOBITES. — A peculiar group of extinct crustaceans, somewhat resembling the woodlice in external form, and, like some of them, capable of rolling themselves up into a ball.

Their remains are found only in the Palaeozoic rocks, and most abundantly in those of Silurian age.

TRIMORPHIC. — Presenting three distinct forms.

UMBELLIFERAE. — An order of plants in which the flowers, which contain five stamens and a pistil with two styles, are supported upon footstalks which spring from the top of the flower stem and spread out like the wires of an umbrella, so as to bring all the flowers in the same head (UMBEL)