Diagnosis (modified from Smalley 1964 b). Gonopod straight, apex folded, spermatic channel emerging on cephalic side, with proximal trianguliform lobe on lateral side. Marginal suture on mesial side, straight along most of stem. Subdistal portion of lateral and cephalic sides with field of minute spines. Distal part with large cephalic lobe and narrow lateral lobe. Field of apical spines weakly developed on internal surface of lateral lobe.
Type species. Allacanthus pittieri Rathbun, 1898 (by original designation).