Dr. J. E. Gray on the Operculum of the Genus Diplommatina. 9 III. — On the Operculum of the Genus Diplommatina. By Dr. J. E. Gray, F.R.S., V.P.Z.S. &c. To the Editors of the Annals of Natural History. Gentlemen, If Mr. Benson, before writing his observations on this genus which appeared in the preceding Number of the ' Annals ' (vol. xi. p. 433), had taken the trouble to come and examine the specimens of Diplommatina in the British Museum on which Dr. Pfeiffer and I had founded our observations, he would have found that there was not the slightest ground for any of the arguments which he has used to induce naturalists to believe that the opercula described as belonging to the genus could have been accidentally placed in the shell, and thus excuse the imper-fection which occurs in his and Capt. Button's description of the animal ; and further, he could never have made the extraordinary suggestion that the opercula belonging to Diplommatina " were adventitious," and might be " assignable to the young Alycceus strangulatus," for the opercula of the two genera are most un-like in structure and colour, and that of the latter genus is at least five times as large as the largest species of the former. The opercula of the three species of Diplommatina costulata in the Museum are each attached to the dry remains of the ani-mal ; two of the animals are still in the shell, and the third was extracted from the shell for the purpose of more accurate exa-mination. It is easy to understand, when we consider the minuteness of the operculum, its small size compared with that of the mouth of the shell, and its transparency, how it may be overlooked, especially when it is sought for in the curious manner mentioned by Capt. Hutton. I have a strong suspicion that if Mr. Benson's specimens were more carefully examined, the operculum would be discovered, unless the animal has been eaten out of the shell by insects. The operculum of Acme fusca, so common in many parts of England, which is of about the same size but darker, was over-looked by many malacologists, and has been denied after it was described by others, as is the case with that of Diplommatina. I may observe, merely to try to clear away certain theoi'ies which continue to cling about malacology, that I cannot consider " the existence of the tooth-like plait on the columella " of any force as " militating against the theory of an operculum " in this genus, for we now well know that Pyramidella, Odostomia and
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