154 Rev. T. Hincks's Critical Notes 



only character left, tlierefore, as the peculium of the Adeonidge 

 is the coexistence (generally) in the colonies of three forms of 

 cell, of which the reproductive seems to be without an exact 

 parallel amongst the Chilostomata. 



But it must be noted that cases commonly occur in which 

 the cell carrying the ooecium exceeds in size the ordinary 

 zooecium and is furnished (like the reproductive cell of the 

 Adeonidaj) with a differently shaped orifice. This condition 

 is strongly marked in such a species as Schizoporella ohliqua^ 

 MacGillivray (sp.), in which there is a striking dissimilarity 

 between the operculum of the ordinary zooecium and that of 

 the reproductive cell. 



In ScMzoporella acuminata, Hincks, the orifice of the 

 gonoecium is about twice as large as that of the zooecium, and 

 assumes a different form. In cases of this kind, before the 

 growth of the marsupium has commenced, the cells destined 

 to discharge the reproductive function are known at once by 

 their peculiarities of structure. In some species of Stegano- 

 porella [S. magnilahris and S. Neozelanica) the structure of 

 the gonoecial cell is materially modified, and there is no 

 external marsupium. 



We have here in a less degree the very specialization of 

 the reproductive function which we find amongst the Adeo- 

 nidse. The development of a class of cells with a modified 

 structure in which the generative products originate is by no 

 means confined to a single family. The character is widely 

 diffused and can hardly, even in its most distinctive form, 

 be made the basis of a fiunily group or warrant the sepa- 

 ration of species which exhibit such an essential identity of 

 zooecial structure as the Microporellidai and a large propor- 

 tion of the Adeonese of Busk. 



There is a strong case then for the union of the latter family 

 with the Microporellidae in a single group, on the ground that 

 the essential characters of the zooecium are the same in both, 

 whilst the differences between them are of common occur- 

 rence amongst the most nearly related forms. On the other 

 hand, the remarkable specialization of the reproductive func- 

 tion amongst some of the Adeonidse, which is assigned in 

 many of the species to groups of peculiarly-constituted cells 

 (subcolonies), distinguished by their size, by the structure of 

 the orifice, and by the enlarged system of pores for the more 

 complete aeration (probably) of the generative products, and 

 the entire suppression of the usual marsupial arrangement, 

 are undoubtedly points of much interest, though not in my 

 judgment of j^rimary systematic importance. 



In a large proportion of cases the clusters of reproductive 



