VIII CLASSIFICATION 247 
or sometimes in the form of a long spine. Cambrian. Genera: 
Olenellus, Holmia, Mesonacis, Olenelloides, Paradoaxides, 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 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 
Fie. 149. — Clenelloides 
; armatus, Peach. Lower 
present. The thorax consists of from fourteen Cambrian, x3. (After 
; Peach. 
to seventeen segments with grooved pleurae, ee 
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. 
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: Ptychoparia, Angelina, Solenopleura, Sao, 
Agraulos (Arionellus), Ellipsocephalus, Protolenus, Olenus, Peltura, 
Acerocare, Hurycare, Ctenopyge, Leptoplastus, Triarthrus, Para- 
bolina, Sphaerophthalmus, Parabolinella, Ceratopyge (position 
doubtful).  Dikelocephalus 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 
