63 



Belfast Museum, containing an individual in all respects, but that of 

 size, quite identical. 



Although the G. niger of Montagu and Jenyns accords better with 

 the description of Linnaeus — consisting only of the number of fin-rays 

 —than the species for which Cuv. and Val. have adopted his name, 

 yet, as several other European Gobies equally well agree with the brief 

 characters in the ' Systema Naturce,' and it being necessary to give 

 one of the two which have been confounded together a new name, 

 it appears to me that the species described as G. niger in the ' His- 

 toire Naturelle des Poissons' of the last-named authors,-—the greatest 

 and most comprehensive work yet attempted on the subject — should 

 retain the term there given it, and that it is to the Gobitis niger oi 

 British authors that the new appellation should be applied. With 

 this view I propose the name of Gobius Britannicus, not to indicate 

 its existence only on the British shores, but in the hope that it may 

 perhaps better than any other term mark it as the species of British 

 authors. 



As M. Valenciennes has observed that " M. Yarrell a public une 

 charmante figure de nutre gobie," (t. xii. p. 18.) it must be added 

 that this figure is more illustrative of my G. Britannicus than what 

 I have considered the G. niger of Cuv. and Val. ; in hypercriticism 

 all it indeed wants to be a perfect representation of that fish is — the 

 lower jaw a little longer, and the teeth smaller, less regular and 

 truncated. 



Mr. Owen then laid before the Meeting the following observations 

 upon the structure of the shell in the Water-clam, {Spondylus varius. 

 Brod.) ? 



Having been led to reflect, while considering the uses of the 

 camerated part of the shell of the Nautilus, upon the degree or ex- 

 tent to which that s'tructure might depend upon the mode of growth 

 of the animal and its shell, and how far it was a necessary physical 

 consequence of the increase and change of position of the animal, in- 

 dependently of any special purpose served by the forsaken parts or 

 chambers of the shell, I have paid attention to all the cases that 

 have come under my observation of the formation of chambers in 

 shells, by the secretion, on the part of the animal, of a nacreous layer, 

 forming a new basis of support to the soft parts, and cutting off the 

 deserted portion of the shell from the chamber of occupation. 



It is well known that this process is not the only mode adopted 

 to suit the shell to the changing form and bulk or other exigencies 

 of its occupant. In the genus Magilus the part of the shell from which 

 the body gradually recedes is filled up by a continuous compact se- 

 cretion of calcareous matter, and a solid massive elongated shell is 

 thus produced, which would be a great incumbrance to a locomo- 

 tive mollusc, but is of no inconvenience to an univalve destined by 

 nature to live buried in a mass of lithophytous coral. 



In Helix dccollata, again, the deserted part of the shell, after 

 being partitioned oflf by the nacreous layer secreted by the posterior 

 part of the mantle, is broken away by some yet unexplained process, 

 and consequently no chambers nor any solid apex of the shell remains. 



