Trigonopeltastes is from trigono, Greek "triangular", and "peltast" which was a shield used in battle in the ancient world. Or peltast may refer to soldiers who used that shield. (Based on Internet searches.)
Numbers
Two species (T. delta and T. floridanus) are listed for North America on the Nearctica (1) checklists. T. floridanus is local to Florida and somewhat rare. T. delta is widespread in the southeastern US.
Woodruff (1960) lists ten species total for the genus, with two in the United States, seven in Central America, and one recorded from Brazil.
Woodruff, R.E. (1960). Suppression of the genus Roplisa Casey, with notes on the United States species of Trigonopeltastes Burmeister. Florida Entomologist 43(3): 139-145 (PDF)