30 F. D. Longe — Oolitic Fohjzoa. 



operculum is said to be attached to the cell wall merely by a portion 

 of its own membrane remaining fixed, and in some cases the oper- 

 culum is placed in the interior of the cell, " deep down in the throat." ' 



It is evident from this account of the different character of the 

 0]iercula in the Lepralidce that the question whether these lids in 

 Diastopora are or are not true opercula, cannot be determined merely 

 by the non-detection of any visible hinge in the cell wall, or other 

 accessory apparatus for moving them. 



While then these authorities fail to furnish any grounds for 

 denying an operculated character and function to these features, I 

 submit that the consideration of the mode in which they make their 

 appearance in the Diastoporidce affords as good evidence of their 

 being opercula, as the conditions in which they appear in many 

 Cheilostomatous forms. 



I may mention here that, though T wish to avoid resting my 

 argument on any unsupported observations of my own, I am quite 

 satisfied from examination of specimens of Alecto granulata, and 

 other living species, that lids of the same character as those in 

 Diastopora are to be found in the less exsert cells of other tubular 

 forms. Jn the specimens which I have examined some of the 

 cells are distinctly closed with transparent lids, while their previous 

 existence in others is shown by their remains giving a jagged 

 appearance to the interior edge of the orifice. The cells in which 

 they are present are only distinguishable from those in which they 

 are not visible, in being shorter or more immersed, and in having 

 their orifices exposed nearer to the surface of the coenoecium. Such 

 observations suggest that their appearance in some cells, and their 

 absence in others, depends simpl}^ upon the extent of the oral 

 prolongation of the cell, and would be fully explained if these lids 

 were opercula. Such an apparatus would naturally be placed 

 immediately above the zoid when retracted, and if placed in such 

 a position in the decumbent and shorter cells, it would appear as a lid 

 covering the orifice. It might or might not be present in the longer 

 tubes ; but if it were present at the same position relative to the zoids' 

 body, it would be so " deep down in the throat " as to be invisible. 

 I am indebted to Mr. Waters for the information that in Entalo- 

 pTiora riigosa, a dendroid form, in which the tubular cells are much 

 extended, they have been found to be closed internally by " a disk, 

 somewhere about where the tube goes out of the coenoecium." This 

 position agrees fully with that which the lids in Diastopora occupy 

 in the shorter and decumbent cells. It is possible that opercula 

 may be present in the shorter cells, and altogether absent in those 

 in which the oral extremity is prolonged. Such coverings are 

 clearly not so much wanted in long tubular cells as they are in the 

 shorter cells, where the proximity of the orifice to the body of the 

 zoid when retracted would render the cell a very imperfect covering 

 unless it was closed or roofed in. And it would appear to be much 

 more reasonable to regard the opercula as features common more or 



1 Proceedings of Lit. and Phil. Soc. vol. xviii. 



