[1241] 
XVII.—On 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 Larvæ of well-known genera, and perhaps confined to species living in 
deep water. By Joux 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. Drennan, R.N., P.R.S. Communicated by Q. Busk, F.R.S., F.L.S. 
Read February 18, 1858. 
IT has been long known that certain genera of Gasteropoda, which are shell-less in the 
adult state, possess both shell and operculum not only while yet within the ovum, but for 
some little time after their liberation, and that ciliated vela 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 shell 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 nueleus, with that of one of our little pelagie Gasteropods also having 
à 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 in the little Gasteropod just referred to, and that its 
lingual ribbon is triserial and constructed on the type of that of Murex, Purpura, Turbi- 
nella, Ricinula, 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 rudimentary, or not at all apparent,—a fact which is 
clearly in aecordance 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 Cypræa 
umbilicata). Without reference to the contained animals, the most acute conchologist 
could only regard Oheletropis Huxleyi and its little oceanic ally as distinct species of 
one genus, although we now know that it would be a violation of the simplest gr 
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, afford 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 dona of x 
close of one stage of development, which had been going forward during the ud = | 
of the active life of the being, but as establishing a basis upon which the characteristic 
lines of growth of the future shell are laid. | : 
Macgillivraia pelagica possesses the labial plates of Natica or Triton, and the lingual 
