ARGON: Six arms of 99 atoms 594 Central tetrahedra 120 ---- Total 714 ---- Atomic weight 39.60 Number weight 714/18 39.66 METARGON (Plate XX, 5, 6 and 7) again shows only an additional seven atoms in each arm. METARGON: Six arms of 106 atoms 636 Central tetrahedra 120 ---- Total 756 ---- Atomic weight ---- Number weight 756/18 42 [Illustration: PLATE XXI.] KRYPTON (Plate XXI, 1 and 4, and Plate XX, 6 and 7) contains the nitrogen "balloon," elongated by its juxtaposition to _b_ 63. The central tetrahedra appear as usual. KRYPTON: Six arms of 224 atoms 1344 Central tetrahedra 120 ----- Total 1464 ----- Atomic weight 81.20 Number weight 1464/18 81.33 META-KRYPTON differs only from krypton by the substitution of _z_ for _y_ in each arm of the star. META-KRYPTON: Six arms of 231 atoms 1386 Central tetrahedra 120 ----- Total 1506 ----- Atomic weight ----- Number weight 1506/18 83.66 XENON (Plate XXI, 2 and 4, and Plate XX, 6 and 7) has a peculiarity shared only by kalon, that _x_ and _y_ are asymmetrical, the centre of one having three atoms and the centre of the other two. Is this done in order to preserve the difference of seven from its comrade? XENON: Six arms of 363 atoms 2178 Central tetrahedra 120 ----- Total 2298 ----- Atomic weight 127.10 Number weight 2298/18 127.66 META-XENON differs from xenon only by the substitution of two _z_'s for _x_ and _y_. META-XENON: Six arms of 370 atoms 2220 Central tetrahedra 120 ----- Total 2340 ----- Atomic weight ----- Number weight 2340/18 130 KALON (Plate XXI, 3 and 4, and Plate XX, 6 and 7) has a curious cone, possessing a kind of tail which we have not observed elsewhere; _x_ and _y_ show the same asymmetry as in xenon.