Mr. William Phillips on the Oxyd of Uranhtm. 119 



Second Modification, 



- This modification consists in a decrease on the terminal edges of 

 the primitive prism, by which each is replaced by a trapezoidal 

 plane, inclining more on the lateral than on the terminal faces j 

 and, as will be obvious on consulting the planes of this modifica- 

 tidns numbered 2. 2, on figs. 23 and 24, tending to produce a 

 very acute octohedron. On the crystals described by figs. 18, 14, 

 15, and 16, the lateral primitive planes have wholly disappeared. 

 The lines on fig. 9 shew the strlse, which, on the larger crystals, 

 are not only visible, but deep. 



Third Modijication, 



The third modification consists in a decrease on the solid 

 angles of the primitive prism, by which each is replaced by 

 an isosceles triangular plane, inclining more on the lateral edge 

 than on the terminal face, fig. 17. The length of the crystals 

 delineated by figs. 23 and 24, which shew the approach to the 

 acute octohedron, would, if the apices of the crystals had been 

 complete, have equalled at least four times their breadth ; they 

 are deeply striated in the direction shewn on fig. 9. I possess 

 a crystal delineated by fig. 24, on which the planes 2.2, are per- 

 fectly brilliant and well defined. Fig. 31 shews the combination 

 of the planes of this with those of the preceding modifications 

 and of the primitive prism. On the crystals described by the four 

 last figures in the series of this modification, two of the four 

 planes of the second modification have disappeared on each pyra- 

 mid, giving to their common base and to their terminal faces the 

 form of triangular planes. 



