Mecyclothorax Sharp 1903: 243 (type species Cyclothorax montivagus Blackburn by Andrewes 1939).
Cyclothorax MacLeay 1871: 104 (not Cyclothorax Frauenfeld, 1868; synonymy Sloane 1903; type species Cyclothorax punctipennis MacLeay by monotypy).
Thriscothorax Sharp 1903: 257 (synonymy Britton 1948; type species Cyclothorax unctus Blackburn by original designation).
Atelothorax Sharp 1903: 269 (synonymy Britton 1948; type species Atelothorax optatus Sharp by monotypy).
Metrothorax Sharp 1903: 269 (synonymy Britton 1948; type species Metrothorax molops Sharp by Lorenz 1998).
Antagonaspis Enderlein 1909: 488 (synonymy Jeannel 1940; type species Antagonaspis sculptopunctata Enderlein by original designation).
Phacothorax Jeannel 1944: 84 (synonymy Liebherr and Marris 2009; type species Phacothorax fleutiauxi Jeannel by original designation).
Loeffleria Mandl 1969: 54 (synonymy Baehr and Lorenz 1999; type species Loeffleria globicollis Mandl by monotypy).
Diagnosis. Mecyclothorax beetles can be distinguished from all other Carabidae inhabiting New Guinea by: 1) presence of a seta near the anterior margin of the mandibular scrobe; 2) glabrous, fusiform apical maxillary palpomeres; 3) antennomeres 1–2 plus the base of 3 without a pelage-like covering of short, fine setae, although the apical half to two-thirds of antennomere 3 may have such a covering; 4) ligula bisetose, with paraglossae free and extended beyond the apical glossal margin; 5) mentum tooth unidentate, its apex broadly to narrowly rounded, its sides obtuse to acute; 6) elytra with interval 7 at most raised as a low ridge, not distinctly carinate, and elytral lateral margin not strongly plicate, the internal plica visible at the subapical sinuation in members of some species, but the lateral margin not distorted by its presence; 7) male protarsal adhesive setae biseriate, present on protarsomeres 1–3, protarsomere 4 bilobed; 8) male ventral or right paramere with two apical setae and setose ventral margin, male dorsal or left paramere elongate, with 2–6 apical setae; 9) female apical abdominal ventrite with four larger marginal setae, two each side, plus a median patch of 4–5 smaller subapical setae.
All species treated in this review are characterized by the presence of both anterior and posterior supraorbital setae. There are two setae present each side of the submentum. The legs are generalized as: 1) fourth tarsomere moderately bilobed, e.g. length of metatarsomere (MT) 4 to apex of outer lobe 1.2–1.5X median length; 2) MT4 with both apical and subapical setae present; 3) tarsomeres dorsally glabrous and convex, shallow lateral sulci present only ventrad as a low, irregular lateral ridge. Where the males are known, they are characterized by the presence of only one apical seta each side of the apical abdominal ventrite.