Plagiohammus Dillon & Dillon, 1941 is considered a junior synonym of Hammatoderus Gemminger & Harold, 1873. Four new species are described: Hammatoderus juliae, from Colombia; H. migueli and H. antonkozlovi, from Ecuador; and H. lingafelteri, from Mexico. Hammoderus spinipennis Thomson, 1860, and Hammoderus quadriplagiatus Breuning, 1943 are placed as junior synonyms of Hammoderus thoracicus White, 1858 (= Hammatoderus thoracicus). Consequently, Hammatoderus jacobyi Nonfried, 1894, synonym of H. spinipennis, is also a junior synonym of H. thoracicus. The synonymy between Hammoderus strandi Breuning, 1943 and Plagiohammus olivescens Dillon & Dillon, 1941 is formally established. Plagiohammus mexicanus Breuning, 1950 is provisionally transferred to Monochamus Dejean, 1821, and the type locality is questioned. Eight types are figured for the first time: Plagiohammus strandi; Plagiohammus mexicanus; Plagiohammus confusor Dillon & Dillon, 1941; Hammoderus spinipennis; Hammoderus quadriplagiatus; Hammoderus inermis (Thomson, 1857); Hammoderus sallei (Thomson, 1860); Hammoderus lacordairei (Thomson, 1860).