THE CEYLOJf PEARL-OYSTER. 337 



It, was about 1-3 mm. ia diameter, and situated in the lx)dy- 

 parenchyma over the ovary (as in the Persian Gulf examples 

 described above). The centre whs a mass of concentrically 

 laminated cohimnar substance, passing over externally into micro 

 *and about 0-5 mm. in diameter. I treat it here provisionally a j 

 a parenchyma-pearl, as there is nothing to suggest that it is a 

 muscle-pearl. 



(b) This^ was a nice little spherical pearl, well out in the 

 mantle. The centre was a spluerocrystal-like body, of the same 

 nature as those shown in figs. 35 & 3G (Pis. XLI. & XLIL). 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 PI. 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 in 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 PI. XXXVI. fig. 13. 

 The pearl is quite close to the mantle-margin, in the musculature! 

 In the centre there is a cavity with a few granular contents. 

 This is surrounded by what appears to be ordinary nacre, then 

 nacre with radial reinforcements, then nacre again. It suo-o-ests 

 a muscle-pearl rather than a parenchyma-pearl. 



(/) 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 7)jlocephalnm 

 viinns. 



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. Unlahelled Pearls {dry) in the British Ilusevm. 



In September 1911 Mr. E. A. Smith, I.S.O., 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 etc.) were those of iM. vulgaris, and the 

 fragments of shell to wliich some of them were attached were 

 undoubtedly referable to this species, and probably to examples 

 from Ceylon (heavily incrusted and much corroded with Clloua). 



Proc. Zool. Soc. — 1912, No. XXII. 22 



