INTKODUCTION. 
XXlll 
In 1893 I followed Busk^ in regarding the small pores in 
Biscaporella LicTienopora') as the openings of cancelli, and 
therefore included the family Discoporellidae in the Cancellata. 
But in 1896 I became very doubtful as to the nature of these 
structures in the Discoporellidm, for many of the pores appeared to 
me to be mesopores, and if so, Discoporella should be included in 
the Trepostomata. On the other hand, in 1896 Harmer ^ published 
his memoir on the development of ‘ Ltchenopora ’ verrucciTia, and 
showed that in the young colony, as far as he traced its history, 
there were cancelli derived from interzooecial spaces, but no 
mesopores. Harmer is emphatic that the alveoli from which the 
cancelli are formed are not suppressed zooecia.^ 
If Harmer’s account be complete, then ‘ Lichenopora ’ verrucaria 
is cancellate, and my opinion in reference to the Discoporellidae in 
1893 was correct. But there are two uncertainties. (1) The 
adult ‘ Lichenopora ’ verrucaria may have mesopores, though none 
had been formed in the young zoaria of which the development 
had been traced by Dr. Harmer. (2) Discoporella Lichenopora’’) 
may contain some species with cancelli and others with mesopores. 
It appears not improbable that such species as D. verrucaria have 
cancelli and others, e.g., D. hispida, D. novcezelandicv, and D. holds- 
worthi, have mesopores. Hr. Waters ^ has objected to the view 
that ‘ Lichenopora ’ and Hornera can be included in the same 
sub-order ; and as regards the three species last-mentioned he is 
probably correct. 
Among the Cretaceous species that have to be considered in 
reference to Lichenopora is the genus Discocavea, which may be 
cancellous and not mesoporous. Unfortunately the attempt to 
decide its structure by the examination of thin slices has failed, 
as the specimens crumbled and were lost in the process of section- 
cutting; and the number of specimens in the collection was not 
enough to justify the sacrifice of more. 
Sections of Radiopora show that it has mesopores and not cancelli. 
^ Busk. B.M. Cat. Mar. Polyz. pt. hi. p. 30. “ Surface cancellated or 
porous” is given as one of the characters of the Discoporellidae. 
S. F. Harmer. “ Development of Lichenopora verrucaria^’’ Quart. Jouru, 
Micro. Sci. vol. xxxix. p. 90. 
3 Ihid. p. 135. 
^ A. W. Waters. Bryozoa : Exped. Antarct. Beige, p. 96. 
