THE CEYLON rEAKL-OYSTER. 333 



of tliose not figured here are retained with the slides for 

 reference.) 



(a) One (Preparation XLV) luid no obvious nucleus or pseudo- 

 nucleus. 



(h) One (Preparation XLIII) had a small sphan-ocrystal-like 

 centre of colunmai- substance, with no foreign contents 

 (PI. XLV. figs. 50 & 50 « and PI. XLI. fig. 35). 



(c) Three (Preparations XL, XLIV, & LIV) had what appenred 

 to be irregular masses of amorphous shell-substance, in 

 central cavities, passing over into repair-substance (PI. 

 XLV. figs. 53 & 53 «; PI. XLVI. fig. 57 ; and PI. XLIL 

 fig. 40). 



{(I) Three (Preparations XLVII, LIII, & LIVc) had central 

 cavities containing moi^e or less granular matter, the 

 character of which could not be determined, but which 

 suggested dead oi-ganic particles (PI. XLV. fig. 52 and 

 PL XLII. fig. 36). This was surrounded by repair- 

 substance of columnar structure. 



(e) One (Preparation LIV j) had in its central cavity granular 

 matter in which diatoms, fragments of sponge-spieules, 

 (?) minute sand-particles, and vegetable debi'is were present. 

 These were surrounded by columnar repair-substance 

 (PI. XLIII. fig. 44). 



(/) One (Preparation LIVe) had, in the otherwise indis- 

 tinguishable granular contents of the central cavity, a 

 fragment of a Radiolarian shell (PI. XLIII. fig. 45). 



((/) Four had undoubted sand-grains, forming the nuclei around 

 which the pearl was laid down (Preparations LII, 

 LIV A, LIVh, & LIVi). The largest diameters of 

 the sand-grains in these four cases measured, respectively, 

 •8 mm., -3 X "15 mm., '6 mm., and -3 mm. (PI. XLV. 

 figs. 54 & 54 a ; PI. XLVI. figs. 55 & 56). 



{h) One (Preparation LIV k) had a large spharocrystal-like 

 pseudo-nucleus of repair-substance, intergrading with 

 nacre, and a central cavity which had been partly 

 obliterated in cutting the sections, but apparently con- 

 tained several small quartz-fragments. 

 (i) Six pearls (Preparations XLII, LI, LIV B, LIV D, 

 LIVg, & LIV f) had, in their centres, bodies which 

 were so hard that they broke away in sectioning, and were 

 unfortunately not returned to me with the sections. The 

 probable diameters of these bodies in the first five pearls 

 were respectively ■45 mm., •2 mm., '1 mm., •25 mm., and 

 •6 mm. Preparation LIV p had a pseudo-nucleus of 

 amorphous substance so dense that it broke away. In the 

 cases of XLII, LIV b, and LIV o, I feel pretty sure 

 that the nuclei here too were grains of sand, the others 

 may have had either sand-grains or abnormally hard 

 amorphous substance in their centres (PI. XLV. fig. 51 ; 

 PI. XLII. figs. 37-39). 



