ff. Fore legs delicate, with very long and slender claws; other legs very stout with short and stout claws; thumb-like process of the tibia short and stout; abdomen very short and broad; segment one to five closely crowded, thus the stigmata of segments three to five apparently lying in one segment; segments five to eight with lateral processes; telson without lateral conical appendages (fig. 69). Crab louse of man. PHTHIRUS PUBIS. dd. Eyes indistinct or wanting; pharynx long and slender, fulturæ very slender and closely applied to the pharynx; proboscis very long. Several genera found upon various mammals. HÆMATOPINIDÆ. cc. Body swollen; meso- and metathorax, and abdominal segments two to eight each with a pair of stigmata; eyes wanting; antennæ four or five-segmented; body covered with stout spines. Three genera found upon marine mammals. ECHINOPHTHIRIIDÆ aa. Legs fitted for walking or jumping; spiracles of abdomen usually ventral; beak segmented. b. Apex of head usually directed anteriorly; beak arising from its apex; sides of the face remote from the front coxæ; first pair of wings when present thickened at base, with thinner margins. HETEROPTERA [Illustration: 159. Taxonomic details of Hemiptera-Heteroptera. (_a_) Dorsal aspect; (_b_) seta from bedbug; (_c_) wing of Heteropteron; (_d_) leg; (_e_) wing of Sinea.] c. Front tarsi of one segment, spade-form (palæformes); beak short, at most two-segmented; intermediate legs long, slender; posterior pair adapted for swimming. CORIXIDÆ cc. Front tarsi rarely one-segmented, never spade-form; beak free, at least three-segmented. d. Pulvilli wanting. e. Hemelytra usually with a distinct clavus (fig. 159), clavus always ends behind the apex of the scutellum, forming the commissure. (Species having the wings much reduced or wanting should be sought for in both sections.) f. Antennæ very short; meso- and metasternum composite; eyes always present. g. Ocelli present; beak four-segmented. OCHTERIDÆ and NERTHRIDÆ. gg. Ocelli wanting; antennæ more or less hidden in a groove. h. Anterior coxæ inserted at or near anterior margin of the prosternum; front legs raptorial; beak three-segmented BELOSTOMIDÆ (with swimming legs), NEPIDÆ, NAUCORIDÆ. i. Metasternum without a median longitudinal keel; antennæ always four-segmented.