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XVII.— Ow the probable Metamorphosis of Pedicularia and other forms ; affording pre- 

 sumptive evidence that the Pelagic Gasteropoda, so called, are not adult forms, but, 

 as it were, the Larvce of well-known genera, and perhaps confined to species living in 

 deep loater. By John Denis Macdonald, Assistant-Surgeon of H.M.S. 'Herald,' 

 employed on Surveying Service in the South-western Pacific, under the command of 

 Captain H. M. Denham, B.N., F.B.S. Communicated by G. Busk, F.B.S., F.L.S. 



Read February 18, 1858. 



It has been long known that certain genera of Gasteropoda, which are sheU-less in the 

 adult state, possess both sheU and operculum not only while yet within the ovum, but for 

 some little time after their liberation, and that ciliated yela precede the more perfect de- 

 velopment of the foot. This is especially true of the Nudibranchs ; and Janthina, which 

 exhibits so near an approach to them in its organization, merely loses the little operculum 

 of its embryonic condition, while the spiral sheU is retained. But a more striking change 

 than this occurs in the case of the genus Pedicularia, if my observations be correct ; for 

 I believe that I have identified the anatomy of a certain species whose shell presents a 

 beautifully cancellated nucleus, with that of one of our httle pelagic Gasteropods also having 

 a cancellated shell, but presenting an aperture so closely resembling that of Cheletropis as 

 to have misled me in naming figures of its labial and lingual dental organs, given in illus- 

 tration of a former paper. I am, however, now in a position to prove that the oral 

 teeth of Cheletropis are not lateral as va the little Gasteropod just referred to, and that its 

 Ungual ribbon is triserial and constructed on the type of that of Murex, Purpura, Turbi- 

 nella, Bicinula, and such genera, — not septiserial as in Pedicularia and the little animal 

 which I believe to be its fry. In the latter case moreover, it must be mentioned that the 

 external series of uncini are often rudimentarj^, or not at all apparent, — a fact which is 

 clearly in accordance with the common law of development of the lingual ribbon (as 

 noticed in a previous paper, with an illustrative figure selected from the fry of Cyjyrcea 

 wnbilicata). Without reference to the contained animals, the most acute conchologist 

 could only regard Cheletropis Huxleyi and its little oceanic aUy as distinct species of 

 one genus, although we now know that it would be a violation of the simplest anatomical 

 principles to place them even in the same family. Here, to a certain extent, similar con- 

 ditions have arisen out of similar necessities in two otherwise very dissimilar beings. 

 The final modelling, and thickening of the lip, moreover, aff'ord no proof whatever that 

 these shells have attained their adult state ; for this change is usual in other cases, as in 

 Carinaria, where its further progress is more easily traced, not only as an indication of the 

 close of one stage of development, which had been going forward during the early part 

 of the active hfe of the being, but as estabUshiag a basis upon wliich the characteristic 

 lines of groAvth of the futm-e shell are laid. 



Macgillicraia pelagica possesses the labial plates of Natica or Triton, and the lingual 



