147 



5. On THE NUCLEUS OF THE OpERCULTJM OF CyCLOSTOMA 



ELEGANs. By John Edward Gray, Ph.D., F.R.S. 



la my various physiological papers I have attempted to establish 

 the fact that the opercula of shells are analogous to the second 

 valve of a bivalve shell, and are in fact a counterpart of the other 

 valve. I have shown that they are formed at the šame time on the 

 body of the Mollusca ; that they have a peculiar mantle, similar to 

 the mantle of the spirai shelį and that they are inereased in size in 

 the šame manner, 



On lately examining the operculum of Cyclostoma elegans, I was 

 struck with the fact (which might have beeu foreseen when the first 

 formation is eonsidered) that they have a somewhat irregular nucleus 

 or first-formed part, likę the nucleus to be observed on the apex of 

 the spire of raost univalve shells, as shown in the accompanying 

 figure, drawn and engraved by Miss Jessie Dunlop. 



I may further observe, that the operculum of this shell is formed 

 of two shelly platės, separated from each other by arched laminse 

 coucentric with the outer edge of the lašt whorl, placed under the 

 concentric grooves of growth on the outer and inner surface, leaving a 

 series of pores on the circumference in the groove between the two 

 platės. 



6. On a Monstrosity of Haliotis (albicans?). 

 By John Edward Gray, Ph.D., F.R.S., P.B.S., etc. 



(Mollusca, PI. XXXIV.) 



Mr. Cuming kindly showed to me a series of four specimens of 

 Ear-shells, which he procured in Paris, and of which he has some 

 other examples. 



The four specimens are all peculiar for having an elongated con- 

 tinued slit occupying the place where the series of perforations are 

 usually situated, — this slit extending more than one-third of the 

 length of the spirai ridges on the outer or left side of the whorls ; 



