350 Miscellaneous. 



species," as expressed, about a year ago, in the 'Annals.' I now 

 write to state that I am preparing a supplement to my ' Notes on 

 Permian Fossils, — Palliobranchiata,' in which the " distinctly and 

 regularly perforated" histological structure of the German species 

 will be more fully described than I have yet done, and proved to be 

 like that "of any Terehratulidcer 



I cannot conclude without expressing my warm appreciation of the 

 trouble which both Mr. Davidson and Dr. Carpenter have taken in 

 this question. 



I am, Gentlemen, 



Yours very truly, 



William King. 



On the Nucleus of the Operculum of Cvclostoma elegans. 

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



In 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 same time on the 

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

 the mantle of the spiral shell, and that they are increased in size in 

 the same manner. 



On lately examining the operculum of Cyclostoma elegans, I was 

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

 formation is considered) that they have a somewhat irregular nucleus 

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

 the spire of most 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 plates, separated from each other by arched laminae 

 concentric with the outer edge of the last 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 

 plates.— Proc. Zoo/. Soc. May 27, 1856. 



