=Fam. 4. Harpedidae= (Figs. 139, G, H; 150, A).—The head is large and has a broad, flat border which is finely punctate, and extends backwards on each side in the form of a horn-like projection nearly as far as the posterior end of the thorax. The glabella is convex and does not reach the front margin. The cheeks are less convex than the glabella, and bear eyes which usually consist of two or three lenses. An eye-line connects the eye with the anterior part of the glabella. A suture is stated to occur at the external margin of the flat border. The thorax consists of from twenty-five to twenty-nine segments; its axis is narrow, and the pleurae are long and grooved. The pygidium is very small, and consists of three or four segments. Ordovician to Devonian. Genus: _Harpes_. [Illustration: FIG. 147.—_Paradoxides bohemicus_, Barr. × ½. Middle Cambrian. (After Zittel.) ] [Illustration: FIG. 148.—_Holmia kjerulfi_, Linnars. × 1. Lower Cambrian. (After Holm.) ] =Fam. 5. Paradoxidae= (Figs. 147, 148, 149).—The cephalic shield is large, and bears long genal spines. The glabella is more or less swollen in front. The facial sutures appear to be absent in some genera, and when present extend from the posterior to the anterior margin. The palpebral lobes are long, and often more or less semicircular or kidney-shaped. The thorax is long, and consists of from sixteen to twenty segments with their pleurae produced into spines. The pygidium is very small, and plate-like, or sometimes in the form of a long spine. Cambrian. Genera: _Olenellus_, _Holmia_, _Mesonacis_, _Olenelloides_, _Paradoxides_, _Zacanthoides_, _Centropleura_ (_Anopolenus_). _Remopleurides_ (Fig. 150, D) from the Ordovician is usually included in the Paradoxidae, but probably belongs to a separate family. [Illustration: FIG. 149.—_Clenelloides armatus_, Peach. Lower Cambrian, × 3. (After Peach.) ] =Fam. 6. Conocephalidae (Conocoryphidae)= (Fig. 150, E).—The cephalic shield is semicircular, and larger than the pygidium. The glabella narrows in front. The facial suture passes from near the genal angle on the posterior border to the antero-lateral margin, and limits a large fixed cheek and a narrow free cheek. Eyes are absent or rudimentary, but an eye-line is usually present. The thorax consists of from fourteen to seventeen segments with grooved pleurae, which may be pointed, but are not usually produced into spines. The pygidium is small, and formed of few segments. Cambrian. Genera: _Conocoryphe_, _Atops_, _Ctenocephalus_, _Bathynotus_.