78 Dr. J. D. Macdonald on the Anatomy of Diplommatina, 



it was too hastily assumed to belong. Dr. Gray, however, as 

 it then appeared, settled the question satisfactorily by the 

 examination of original specimens in which an operculum was 

 undoubtedly present. At the time the number of the 'Annals ' 

 containing his letter came into my hands, I was employed in 

 the South Seas*, and, being well acquainted with three dis- 

 tinct species of Diplommatina occurring at Lord-Howe Island, 

 I thought I might readily furnish Dr. Gray with drawings of the 

 shell, operculum, and animal of those species, should his argu- 

 ment require further support. Nevertheless, on visiting the 

 island of Vatoa, Feejee group, I was not a little surprised to 

 find a very minute and smooth pupiform shell, with dextral 

 turns, thickened double peristome, and a tooth on the colu- 

 mellar lip, containing an animal in every particular identical 

 with that oi Diplommatina save the operculum, of which I did 

 not discover a trace, though the cicatrix of the operculigerous 

 lobe was distinct enough, as shown in the figures (1 & 2 1?, 

 PI. IV). The above-mentioned question immediately recurred 

 to my mind, and I also reflected how far are shell-characters 

 to be trusted in the establishment of genera, and how wide is 

 the latitude within which specific distinctions may range. I 

 sympathized with Mr. Benson ; for, according to my own ex- 

 perience, not only in this case but in numerous other Feejeean 

 species, if the operculum be present at all, it must be in a very 

 rudimentary state. 



Conchologists might prepare a new genus for the reception 

 of the little shell just noticed, which exhibits but few points in 

 common with the known Diphmmatince'^ yet even this would 

 not shake my faith in a conclusion the truth of which is most 

 evident to my own mind, namely, that the occupant is Di- 

 plommatina^ name the dwelling what you please. In sub- 

 stantiation of this view, I may mention that of eight or nine 

 new Feejeean species of the genus, all of which are sinistral, 

 some have simple peristomes, others tooth-like processes in 

 the aperture, and the latter is constricted, expanded, or more 

 or less ascendent, as the case may be ; but the animals are in 

 all instances similar, or only exhibit specific differences. Al- 

 though the generic characters of Diplommatina are now more 

 comprehensive than they originally were, there appears to be 

 a too great readiness on the part of pure conchologists to found 

 new genera upon any shells that are not conformable in every 

 minute particular with the primary description, which in the 

 nature of things cannot be supposed to be infallible. 



In the mountain-country of Na Viti Levu I found at least 



• In H.M.S. ' Plerald,' Captain, now Admiral, Sir H. M. Denham, K.C.B. 



