The skeleton and musculature ofTrigonognathus kabeyai are described in detail. The particular jaw dentition suggests thatTrigonognathus has a clutching-type feeding action. Several characters that might serve this function are discussed from the point of the functional morphology. The phylogenetic relationships ofTrigonognathus are not fully resolved, but it possesses three of the four synapomorphies of the Etmopterinae, i.e., two separate labial cartilages, no supraotic shelf, and prespinal radiais. Furthermore, three equally probable hypotheses ofTrigonognathus relationships, a sister relationship with all etmopterine genera,Etmopterus+Miroscyllium, andAculeola+Centroscyllium, are discussed.