12 CALIFORNIA ACADEMY OF SCIENCES. 



of s to A> an d furthermore I have carefully adjusted the zone t 

 (oo P 2) : y (P) on the goniometer and found that /\ is not in it 

 as it should be were it identical with a. 



o (2 P 2) is never large and is often exceedingly small. It is 

 easily determined by the zones v (2 P) : h (2 P oo) and c (P oo) : 

 y (P). It is absent from only five crystals of the twenty-eight 

 examined. 



s (3 P |) is also very common and usually extremely small on 

 the edge d (2 P 2) : s (oo P). It is determined by the zones d : 

 s and v (2 P) : h (2 P oo). 



Q (4 P 2) is a minute triangular face, found on only one crystal 

 (represented in Fig. 5, PI. II). This crystal is one of the very 

 few that are partially developed on both ends. Q is determined 

 by the zones v (2 P) : £ (3 P |) and a (2 P oo) : x (3 P 3). The 

 observed angle Q : s = 171° 55' ca. agrees very well with its 

 calculated value 171° 59'. 



r (i P |) (Fig. 2, PI. I.) whenever present is always very mi- 

 nute on the edge d (2 P 2) : y (P). It is determined by the zones 

 d : y and v : c. While present as an actual face on only five crys- 

 tals, it is involved in the striation of y and d on many of the 

 others. 



d (2 P 2), determined by the zones v (2 P) : a (2 P oo) and y 

 (P) : y (P), is usually present as a narrow face on the edge v : a. It 

 rarely attains the size represented in Figs. 6, PI. II, and is often 

 extremely small. When v (2 P) is very small, e (3 P §) absent, 

 and d comes to intersection with s (oo P), it takes the form of a 

 very acute lozenge bounded by v, c, a and s. I have already re- 

 ferred to the striation on this face parallel to the edge d : y. 



x (3 P 3), usually very small, attains considerable size but 

 once (Fig. 2, PI. I). It is determined by the zones d (2 P 2) : 

 y (P) and a (2 P oo) : s (oo P). From the two faces of x on the 

 fragment represented in Fig. 7, PI. II, faultless reflections were 

 obtained, givirig x : x (over plane of symmetry) = 66° 39' 40" 

 (calculated 66° 47' 10"), a variation from the calculated value 

 considerably less than that observed between equivalent angles 

 on different crystals in a number of instances. On the same 

 fragment was obtained d : x = 168° 42' (calculated 168° 42' 57"). 



