468 Dr. Gray on the Abnormal Operculum of Polydonta elegans. 



XL. — On the Abnormal Operculum 0/ Polydonta elegans of New 

 Zealand. By Dr. J. E. Gray, F.R.S. &c. 



In the ' Annals and Magazine of Natural History ' for May 1854, 

 N.S. vol. xiii. p. 419, I described the reproduced operculum of 

 a FusuSj fig. 1, and the restored operculum of Pleurotoma baby- 

 lonica, showing that the restored operculum and the mended [)art 

 of one only partially destroyed differed from the normal form of 

 the operculum of the species. 



At that time I had not observed the same fact in opercula of a 

 spiral form. In an interesting collection of shells and other 

 animals made in New Zealand by Dr. Andrew Sinclair, the late 

 Colonial Secretary of that colony, I found a specimen of Poly- 

 donta elegant with a very abnormal operculum ; arising, I have 

 little doubt, from the operculum having been entirely destroyed 

 by some external violence and reproduced by the animal. 



The reproduced operculum is circular, 

 of the size of the mouth of the shell, but 

 instead of being formed of numerous 

 narrow, very gradually enlarged whorls, 

 it has a rather large central circular 

 part or nucleus, which extends into 

 a broad, rather rapidly enlarging whorl 

 and a half, somewhat like the oper- 

 cular or the more circular-mouthed Reproduced operculum of 

 Littorinidce. Polydonta elegans. 



I may observe, that though I have examined all the opercula of 

 shells that have come under my notice for years, I have never 

 seen any example of reproduction of the operculum in the Tro- 

 chidce before ; but according to the following paragraph, extracted 

 from Mr. Clark's ' Marine Mollusca,' p. 309, it is not uncommon 

 in Trochus lineatus : — " A singular character is attached to this 

 species, which I have not observed in any other Trochus. The 

 animal either casts the operculum, or is deprived of it by the 

 attacks of enemies, perhaps from its own pulli, white masses of 

 which, in the genial season, I have seen deposited on the foot, 

 and they may possibly feed on and destroy it ; howev<^r this may 

 be, numerous examples are found with the opercula in various 

 stages of development and renewal, but never resembhng the 

 original : this is a curious fact, which I can at present scarcely 

 account for on rational grounds. The renewals and reparations 

 form irregular spiral, oblique and elliptical curves, or, instead of 

 the sixteen normal volutions, often only show two grossly spiral 

 ones, as in the Littorina littorea. I have many such in my 

 collection. I may observe, that, however the sculpture of the 



