Mr. W. Clark on British Mollusca. 411 



figure to a point of certainty which I think it will be difficult to impeach. 

 I have softened many of these minute creatures in their shells ; and 

 by bruising the anterior portion and carefully removing the spoil 

 from the head and neck, 1 have seen the short, broad, triangular, 

 divergent tentacula, with the very large eyes fixed at the centre of 

 their bases, brought so prominently to view by moisture, and in such 

 fair relief, that it was impossible to have any doubt as to the presence 

 of tentacula as described and figured by Philippi. I was so struck 



with this interesting sight, that I obtained the ^ 



assistance of an excellent lady-artist, to give V^ITV/ " eyes**"*^* 

 me, by the aid of the half-inch object-glass Y\ I-^/t" " *'°^y 

 of the microscope, the sketch, of which the \\jj f ^^^'^^^ 

 woodcut is a copy, verv largely magnified, minus \ '•—— ^°°* 



the cilia, which, from" their delicacy, were in- \ W "p"'"'^"'"" 



visible from collapse ; she produced in a few \ / 



minutes, from her own view, an almost fac- \J 



simile of Philippi' s figure. The head, which 

 undoubtedly exists, was hidden under the mantle ; but its presence 

 was betrayed by the minute tumour. It appears quite clear that 

 Mr. Jeffreys has delineated his animal with rounded lobes, or, in 

 other words, with the tentacula retracted, instead of those described 

 above, and figured in the woodcut as protruded. Mr. Jeifreys's de- 

 scription of the animal is also contrary to its organization, in stating 

 that the eyes are fixed on the "veil" (mantle) : this is not so, though 

 these and the tentacula, being seen through the tenuity of the " veil," 

 have the appearance of being fixed on it ; but the body, head, foot, 

 the eyes, and tentacula form no part of the veil or mantle, which is 

 only their envelope when they are in retraction and quietude, and 

 from whence they are protruded when in action. 



Mr. Jeffreys, in his miscellaneous remarks, charges Philippi with 

 more mistakes respecting the animals of Truncatella trvncatula and 

 T. littorea. I beg to say I have examined both alive, and fully de- 

 scribed them in my *Brit. Mar. Test. Moll.,' and I find that Philippi 

 is correct, except in saying ''operculum simplex, non spirale." But 

 surely the most fastidious can hardly find fault with so venial an 

 error, when the objects are so minute as scarcely to be visible with 

 the naked eye ; they do not exceed in length more than from 4:V^h 

 to -^^ih. of an inch ; and we must recollect that the optical appliances 

 of his time were very inferior to those of the present day. 



With respect to T. atomus. I may state that the excellent view of 

 the organs I have succeeded in obtaining from the moistened speci- 

 mens enables me to say, without doubt, that it is, as Philippi states, 

 a congener of T. truncatula, T. littorea, and, I think, of Assiminia 

 Grayana. (See my * Brit. Mar. Test. Moll.') I will now mention 

 some of the coincidences of this little tribe : the tentacula of all are 

 of a precisely similar character — very short, broad, and triangular, 

 being united at their bases, with the very large eyes inserted in them, 

 at varying distances from their points — not on prominences ; the 

 characters of the operculum agree in all, being, even in the globoso- 

 conic and discoid, somewhat elongated, with, at the base, a pauci- 

 spiral 1^ volution, and finely striated to a point short of the outer 



