8 Mr. W. Clark on the Genus Truucatella. 



It will be seen that this account is essentially the same as the 

 one in the ' British MoUusca/ except that the learned authors 

 have proposed to deposit it in Assiminia. I think its generic 

 position is with Truncatella. A comparison of the two species will 

 show that they are not only identical in the principal characters, 

 but almost all the minutise are congruous. Indeed I may say, 

 that these gentlemen differ little more from me than in the name, 

 * Assiminia,' which I would gladly accept for Truncatella for the 

 reasons below, if such a change in nomenclature were not for- 

 bidden by strict conventional laws. As far as I can learn, not 

 having seen the animal of A. Graijana, the genus Assiminia 

 scarcely varies, if at all, from Truncatella ; at least the generic 

 characters given in the ' British Mollusca ' are absolutely those 

 of that genus, except some difference in the position of the eyes, 

 which I shall not be surprised to find turns out greater in terms 

 than in reality. 



I wish some naturalist would send me here some live examples 

 of A. Grayana ; they inhabit the Greenwich and other eastern 

 marshes about London : if sent by post the same evening when 

 taken, in a small, strong, wooden, turnedhon. of the size of half-a- 

 crown, with a little weed or dry moss only slightly moistened in 

 the water of their habitat, they would probably arrive sufficiently 

 lively for examination. Even the shells, if with the opercula, 

 would enable me to give a qualified opinion on their position. 



The generic title of Truncatella is objectionable, as being in 

 this case too distinctive, and therefore only strictly applicable to 

 Truncatella Montayui, whilst two, if not three, of our indigena, 

 T. littorea, T. Grayana ?, and T. nifidissima ?, are never truncate 

 at the apex ; still, this appellation has been so long established, 

 that it is better to continue it than add new names to science : — 

 the latter reaiarks are M. Philippi's sentiments. We have here 

 a striking illustration of the value of conchological made genera, 

 as, in consequence, three species of one genus have received as 

 many generic titles, from their shells exhibiting a subcylindrical, 

 a conical, and a discoid form (if the Skenea? nitidissima of authors 

 is the T. atomies'? of Philippi, as is probably the case). 



I see no reason to doubt M. Philippi's Truncatella littorina 

 (Moll. Sicil. vol. ii. p. 133. tab, 24. fig. 2) being our present spe- 

 cies ; the description and figure entirely accord. 



It is stated by me in a former paper in the ' Annals ' that this 

 is an apocryphal British species ; — the refutation is now suffi- 

 ciently complete. 



I am. Gentlemen, 



Your most obedient servant, 



AViLLiAM Clark. 



