Mr. J. G. Jeffrey's Notices of Piedmontese MoUusca. 271 



considered of sufficient value to entitle the animal to represent 

 a distinct Trochidan genus, and to nullify its indisputable generic 

 essentials with the type, Truchns, in which we are of opinion it 

 ought to be deposited, instead of burdening science with the 

 new genus Scissurc/la. 



There can be no species of Scissurella without an o])erculuni, 

 as its animal has now been proved to be a Trochidan, all of 

 which are invariably operculated. When that appendage has 

 escaped notice, it has probably been in consequence of the ex- 

 treme tenuity of the fabric of its pellicle, and the want of proper 

 optical power. 



The ciliated lateral vibracula of the Trochidan animal vary 

 from two to four on each side, but are usually three. They 

 are frequently doubled u]), and lie under the flaj) of the upper 

 lobe of the foot ; and, from their slenderncss and change of 

 position, are often difficult to detect. This remark is made to 

 meet the possibility of the vibracula in Mr. Barrett^s Scissurella 

 turning out to be three on each side. 



In conclusion I beg to observe, that malacologists are under 

 great obligations to Mr. Barrett for having solved a long-desired 

 question, and it would be well if other observers would imitate 

 him. I will throw out a hint connected with the present inquiry 

 by mentioning, that it is a great desideratum to obtain notes on 

 the living Trochus subcarinatus of Montagu {Adeorbis, nonnull.), 

 which I have in vain sought for during forty years, and the ac- 

 quisition of which Professor Forbes particularly recommended 

 to my attention. 



Tt is impossible for a single naturalist, however diligent, to do 

 everything and be everywhere ; it is only by the many, seizing 

 the opportunities in their respective localities, that science can 

 be made acquainted with facts to elucidate the unsolved problems 

 in natural history. 



I am. Gentlemen, 



Your most obedient Servant, 



William Clark. 



XXIII. — Further Notices of Piedmontese MoUusca. 

 By J. Gavyx Jeffreys, Esq., F.R.S. 



Scissurella. — Having, in consequence of Mr. Barrett's descrij)tion 

 of the animal of .S*. decussata, D'Orb. {crispata of British autliors), 

 in the last number of the ' Annals,' placed under a microscope some 

 S. eleyans, containing the dried animals, I succeeded in detecting a 

 circular operculum in three out of 14.0 specimens ; and I have also 

 examined the operculum in the Norwegian specimen dredged by 

 Mr. MacAndrew. It resembles the operculum of Trochus (sub-genu3 



