CLASSIFICATION 



247 



Cambrian, x 3. 



(After 



or sometimes in the form of a long spine. Cambrian. Genera : 

 Olenellus, Holmia, Mesonacis, Olenelloides, Paradoxides, Zacan- 

 thoides, Centropleura (Anopolenus). Remo- 

 pleurides (Fig. 150, D) from the Ordovician 

 is usually included in the Paradoxidae, but 

 probably belongs to a separate family. 



Fam. 6. Conocephalidae (Conocory- 

 phidae) (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 an tero- 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, Ctenocephcdus, Batliynotu.s. 



Fam. 7. Olenidae (Figs. 142, 143 ; 150, B, C). The cephalic 

 shield is larger than the pygidium. The glabella is either rec- 

 tangular or parabolic. The facial suture passes from the posterior to 

 the anterior margin. The palpebral lobes are of moderate or rather 

 large size, and are connected by an eye-line with the front part 

 of the glabella. The thorax includes from eleven (occasionally 

 fewer) to eighteen segments with grooved pleurae. The pygidium 

 is usually small, with from two to eight segments. Principally 

 Cambrian. Genera: Piychoparia, Angelina, Solenopleura, Sao, 

 Agraidos (Arionellus), Ellipsoceplialus, Protolenus, Olenus, Peltura, 

 Acerocare, Eurycare, Ctenopyge, Leptoplastus, Triarthrus, Para- 

 lolina, Spliaerophthalmus, Parabolinella, Ceratopyge (position 

 doubtful). Dikdocephalus is usually placed in the Olenidae, but 

 perhaps belongs to a distinct family. 



Fam. 8. Calymenidae (Figs. 136, 137). The glabella is 

 broadest behind. The facial suture starts at or near the genal 

 angle sometimes on the posterior border just inside the angle, 

 sometimes on the lateral border just in front of the angle ; the 

 suture may be continuous with the other suture in front of the 

 glabella, or may cut the anterior margin, beneath which it is 



