410 Mr. W. Clark on British Mollusca. 



from Hayle in Cornwall, are, I think, only large examples of the 

 common M. edulis, of which that gentleman sent me a large valve 

 from Exmouth to compare with them. I could not, however, per- 

 ceive any differences beyond those slight ones that are always to be 

 seen even in the same species. I may observe that the animal of 

 the Mytili varies greatly, from the influence of locality and from the 

 changes of aspect arising from the different seasons of the year, — so 

 much so, indeed, that the mere conchologist often mistakes two phases 

 of the same for distinct species. 



I now come to the '* Gleanings" in the February * Annals' for 

 1859, 3rd series, vol. iii. pp. 106-120. 



Jeffreysial Gulsonce. This is my Chem. Gidsonce, the shell of 

 which I described in the second series of the * Annals,' vol. vi. 

 p. 458, and the animal in vol. viii. p. 108 of the same series. I am 

 quite at a loss to discover upon what principle Mr. Jeffreys (even 

 with a ? affixed) has placed in his own genus this species, first 

 published by myself. Mr. Jeffreys has only examined the shell ; but 

 I have seen both the shell and the animal ; and though the torpidity 

 of the latter did not allow me to be so certain of its characters as I 

 could wish, still I am enabled to say, positively, that it is not a Jef- 

 freysitty as the operculum of that genus is of a very peculiar form, 

 and differs decidedly in structure from that of my Chemnitzia Gul- 

 sonce. 



Euom/phalus nitidissimus {Skeiieal nitidissima of British authors). 

 Mr. Jeffreys also states that he has no doubt it is the Truncatella 

 atomus of Philippi, Moll. Sicil. ii. p. 134, pi. 24. f. 5. I do not believe 

 that so accurate an observer has committed the blunder attributed to 

 him by Mr, Jeffreys, of having described and figured his animal with 

 tentacula, if they had not existed, I think that gentleman is in 

 error, and I shall show that he has done Philippi an injustice ; and I 

 have no doubt, on some subsequent re- examination of the animal of 

 the T. atomus, it will be found to accord with his indices. Every one 

 knows the deceptive appearances of minute creatures, from the effects 

 of light, water, and their constant vibrations, when under microscopic 

 examination. From the mention of the cilia in Mr. Jeffreys's report, 

 I very much think that the tentacula of his animals (at all times '' per- 

 brevia,''' teste Philippi) were not protruded ; for if they had been, 

 the cilia would have clothed them — as in the Rissoce and most other 

 Gasteropoda, which have these delicate aids, for tact, of greater or 

 less length ; and in consequence, the long terminal cilia alone on 

 each side of the rounded lobes, as figured, were visible. 



I have observed that, though animals may apparently be lively, 

 sulkiness or their will often predominates as to particular organs : 

 in the Chemnitzice and RissocB the tentacula are often retracted ; and 

 I have watched for hours before I could obtain a view of them, their 

 cilia being only visible at their terminations ; these, in some species, 

 are very long, of which fact I have pointed out examples in my 

 ' Brit. Mar. Test. Moll.' I am surprised to find that Mr. Jeffreys was 

 not aware that any moUusk possesses the peculiar cilia that fringe 

 the veil or anterior part of the head of this animal. 



I will now proceed to corroborate the correctness of Philippi' s 



