Length 12-15 mm (Hyperia crassa 1). Head unusually large, longer than pereonites I-III combined, in lateral view much longer dorsally than ventrally. Pereonite II higher than others, pereonite VII lowest, anteriorly concave, posteriorly convex; pereonites II, III and IV with transverse folds. Epimeral plates with pointed posteroventral corners; posterolateral margin of pleonite III only weakly convex. Proximal ART of mandibular palp much shorter than distal ART; incisor with 9 or 10 teeth. ART of P I-II with well-developed spines (Hyperia crassa 2), ART 2 of P I with very convex anterior margin. P III and IV with very few spines on posterior margin of ART 4 and 5, P V-VII unarmed. ART 2 fairly narrow in P V-VII. UR II and III with very broad basipodites and endopodites (Hyperia crassa 3). (After original description of Bowman, 1973).