CLINOHEDRAL  CLASS (Hemihedral; Domatic) . Crystals of this class are symmetrical only with respect to a single

plane . The only form which is here geometrically the same as in the holosymmetric class is the clino-pinacoid {o10} . The forms perpendicular to the plane of symmetry are all pedions, consisting of single planes with the indices (100), (Too), (o01), (ooi), (hol), &c . The remaining forms, {hko} ,(okl) and (hkl), are domes or " gonioids " (yc,via, an angle, and elbos, form), consisting of two planes equally inclined to the plane of symmetry . Examples are potassium tetrathionate (K2S406), hydrogen trisodium hypophosphate (HNaaP208.9H2O); and amongst minerals, clinohedrite (H2ZnCaSiO4) and scolectite . 5 . ANORTHIC SYSTEM (Triclinic) . In the anorthic (from av, privative, and bpOos, right) or triclinic system none of the three crystallographic axes are at right angles, and they are all of unequal lengths . In addition to the parameters a : b : c, it is necessary to know the angles, a, ft, and y, between the axes . In anorthite, for example, these elements are a : b : c= 0.6347 : I :0.5501; a=93° 13', 19=115° 55', 7=91° 12' .