Examples from the Web for trigonal
Parietes ribbed, mottled purplish-red; orifice broad, trigonal, hardly toothed.A Monograph on the Sub-class Cirripedia (Volume 2 of 2)|Charles Darwin
The horns are trigonal, laterally compressed and knotted on the upper edge.Natural History of the Mammalia of India and Ceylon|Robert A. Sterndale
The leaves are trigonal; they are very short, and they are laid over each other like scales in four rows.Botany for Ladies|Jane Loudon
Trigonal trapezohedron (fig. 74), bounded by six trapezoidal faces.
The cartilage placed in a trigonal pit with a small external ligament.A Conchological Manual|George Brettingham Sowerby