276 PROCEEDINGS OF THE MALACOr.OGICAL SOCIETY. 



The author is uiider the impression tliat they are also formed around 

 parasites that invade the shell-forming area from outside by boring 

 through the shell, as, for example, a boring sponge or mollusc. 



Pearl blisters ■will be found to contain a true pearl, while the 

 other kind of blister is usually hollow or contains some dried organic 

 matter or sand. 



The question suggests itself whether the large growths under 

 discxission are similar in origin to the latter form of ' blister '. It 

 must be admitted that in the largest hollow blister the author has 

 examined the cavity was not very large proportionately to the size of 

 the blister, and its walls were very thick, while the reverse is the case 

 in the monstrous growths under consideration. Nor do the latter give 

 the impression of having been formed round an intruding body. The 

 stalk-like portion of the smaller growth is very curious, and suggests 

 an organic connexion with some body or surface — a condition not 

 found, of course, in the case of ' blisters '. 



It must be admitted that examinations of sections of these 

 monstrosities do not reveal a histological structure compaiable to that 

 of Iridacna, though, if these growths are pathological, one would not 

 expect a close sirailaritv to the normal histologv of that genus. 



Dr. Smith Woodward, F.R.S., and Dr. C. W. Andrews, F.R.S., 

 have drawn the author's attention to the peculiar fact that the 

 interior surface of the larger specimen is seamed with shallow 

 meandering grooves, that give it the appearance of having been 

 formed rouml or applied to some tumour-like growth covered with 

 superficial blood-vessels. 



To conclude, we may- hazard the guess that these specimens are 

 referable to Tridacna, and possibly comparable to ' blisters ' of the 

 pearl oyster, but qualify our identification with a desire for further 

 information on this subject. 



The author desires to express his indebtedness to Mr. F. Spencer, 

 of Hattoii Gardens, who was good enough to exliibit to him his 

 excellent series of ' blisters ' in Meleagrina mar gar it if era. 



Postscript. — The author understands that a suggestion was developed 

 at the meeting of the Society at which this paper was read (when 

 he was unfortunately unable to be present) that these growths might 

 be some form of Cetacean ear-bones. As the nature of these 

 monstrosities is still sxih judice, the author welcomes every suggestion 

 that may be helpful, but the aragonite composition of the growths is 

 sufficient, according to his view, to counterbalance a purely superficial 

 resemblance to the ossicles in question. 



