THE CEYLON PEARL-OYSTER. Sob 
Tt was about 1°3mm. in diameter, and situated in the body- 
parenchyma over the ovary (as in the Persian Gulf examples 
described above). The centre was a mass of concentrically 
laminated columnar substance, passing over externally into nacre 
and about 0-5 mm. in diameter. I treat it here provisionally as 
a parenchyma-pearl, as there 1s nothing to suggest that it is a 
muscle-pearl. 
(6) This was a nice little spherical pearl, well out in the 
mantle. ‘The centre was a spherocrystal-like body, of the same 
nature as those shown in figs. 35 & 36 (Pls. XLI.& XLII). There 
were no recognisable foreign contents, 
(c) This showed a pearl in the parenchyma over the ovary, as 
in the Persian Gulf specimens, with, apparently, all the characters 
of a ‘ fine pearl.’ It had a large dark pseudo-nucleus, 0-4 mm. in 
diameter, much like that shown on Pl. XLVI. fig. 57. There was 
a central cavity, 0°025 mm. in diameter, containing a small 
granular mass; this was followed by nacre, then stratified 
columnar substance, then nacre again. 
(d) Showed two pieces of free mantle, sectioned, one with one 
and one with two pearls iz situ. In the case of the former the 
pseudo-nucleus was incomplete, but could be seen to be composed, 
in part at least, of columnar repair-substance. In the other 
specimen, both pearls had centres resembling those in Dr. Kelaart’s 
material, and may well have been muscle-pearls. 
(e) The central part of this pearl is shown on Pl. XXXVI. fig. 13. 
The pearl is quite close to the mantle-margin, in the musculature. 
In the centre there is a eavity with a few granular contents. 
This is surrounded by what appears to be ordinary nacre, then 
nacre with radial reinforcements, then nacre again. It suggests 
a muscle-pearl rather than a parenchyma-pearl. 
(f) Contained a pearl, near the mantle-margin, the pseudo- 
nucleus of which was not complete. It consisted of alveolar- 
columnar matter; its centre could not be made out. 
This preparation also contained an example of Z'ylocephalum 
minus. 
The remainder of the pearls in Prof. Herdman’s collection, four 
in number, appeared to be incomplete preparations, as no nuclei 
or pseudo-nuclei could be observed. 
D. Unlabelled Pearls (dry) in the British Museum, 
In September 1911 Mr. E. A. Smith, 1.8.0., allowed me to 
examine four dry pearls, from a small collection of pearls and 
attached pearls and blisters, preserved in the Mollusca cabinets 
at the British Museum. 
These specimens were unlabelled and without history, but their 
general characters (colour ete.) were those of J/. vulgaris, and the 
fragments of shell to which some of them were attached were 
undoubtedly referable to this species, and probably to examples 
from Ceylon (heavily incrusted and much eorroded with Cliona). 
Proc. Zoou. Soc.—1912, No. XXII, 22 
[49j 
