117 



Mr. Broderip conjectures that Clavagella may be in its very young 

 state a free Bivalve, floating at large until it arrives at some vacant 

 hole that suits it, when it attaches one valve to the wall of the hole, 

 and proceeds to secrete the tube or siphonic sheath, to enlarge the 

 chamber according to its necessities, and to secrete the shelly per- 

 forated plate which is to give admission to the water at the prac- 

 ticable part of the chamber. The excavation may probably be as- 

 sisted by the secretion from the glands observed by Mr. Owen, and 

 evidently cannot be effected in the greater end of the chamber by 

 mere mechanical attrition ; but the solvent secretion must be one of 

 extensive powers to act on such diflferent substances as siliceous 

 grit, the coral of an Astraopora, calcareous grit, and argUlo-calca- 

 reous tufa, in which respectively were found the Clav. Australis, 

 Clav. elongata, Clav. lata, and Clav. Melitensis. 



Adverting to the different depths at which these several species 

 were found, which varied from near low- water mark to sixty-six feet, 

 Mr. Broderip remarks, that inferences as to the state of submersion 

 of a rock during the lifetime of the fossil species which there occur, 

 ought consequently to be made with caution by the geologist. 



In conclusion he observes, that though the genus Clavagella is in 

 its recent state at present rare, it is in all probability widely dif- 

 fused ; and suggests to collectors a careful examination of masses 

 of coral and submerged perforated rocks with a view to the further 

 elucidation of the habits and structure of these and other interest- 

 ing animals. 



