=Fam. 7. Olenidae= (Figs. 142, 143; 150, B, C).—The cephalic shield is larger than the pygidium. The glabella is either rectangular 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_, _Eurycare_, _Ctenopyge_, _Leptoplastus_, _Triarthrus_, _Parabolina_, _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 connected with the other suture by means of a transverse suture (Fig. 137, B, D). The eyes are rather small. The thorax consists of thirteen segments with grooved pleurae; the pygidium of from six to fourteen segments. Ordovician to Devonian. Genera: _Calymene_, _Synhomalonotus_, _Homalonotus_. [Illustration: FIG. 150.—=A=, _Harpes ungula_, Sternb., Ordovician. =B=, _Ellipsocephalus hoffi_, Scloth., Cambrian. =C=, _Olenus truncatus_, Brünn., Cambrian. (After Angelin.) =D=, _Remopleurides radians_, Barr., Ordovician. =E=, _Conocoryphe sulzeri_, Barr., Cambrian. =F=, _Illaenus dalmanni_, Volb., Ordovician. =G=, _Proëtus bohemicus_, Corda, Silurian, × 1½. =H=, _Aeglina prisca_, Barr., Ordovician, × 3. =I=, _Phacops sternbergi_, Barr., Devonian. (=A=, =D=, =E=, =G=, =H=, =I=, after Barrande; =B=, =F=, from Zittel; natural size except =G=, =H=.) ]