BRYOZOA FROM AUSTRALIA. 675 
form of the cell or zocecium, together with the shape of the aperture 
(which is, perhaps, best indicated by the shape of the operculum) ; the 
presence, in a large number of cases, of a suboral pore or suboral 
avicularium, giving, in their various modifications, useful characters ; 
and the position and nature of the avicularian and vibracular appen- 
dages furnish further means of recognition, though their presence or 
absence does not seem in all cases to be of much importance. 
Besides these we have the ovicell, which by its form frequently gives 
most valuable characters; and the shape, position, and number of 
the rosette-plates are also, where available, of the greatest value. 
Before turning to the description of the Australian Cyclostomata, 
I have, during the last few years, spent a great deal of time in 
examining whether there are not other characters, besides the mode 
of growth, which may be used; and although the results are not 
encouraging, yet by means of more caret observation I believe 
that it will ultimately be possible to arrive at a more natural system 
than obtains at present. It will be best to consider the structures as 
far as possible in the same order that was adopted in discussing the 
characters of the Chilostomata, 
The zocecia being all tubular and quite simple, there is no varia- 
tion here corresponding to the various shapes of the Chilostomata ; 
and again, as the form of the aperture is always round or slightly 
elliptical, the only character here available is that of size (pointed 
out as useful by Smitt some years ago), which seems to be fairly 
constant in the same species. The variation in size is not very 
great, ranging only from about 0°03 millim. to 0:2 millim. in all 
species measured, but anything greater than 0°16 millim. or less 
than 0:07 millim. is very exceptional. There is also no operculum, 
which gives such useful characters in the operculated division ; but, 
on the other hand, the zocecial tubes are closed up by a calcareous 
plate, usually at a short distance from the aperture; and in a paper 
on the ‘“ Closure of the Cyclostomatous Bryozoa ” (Journ. Linn. Soc. 
vol. xvii. p. 400, pl. xvi.), I have pointed out that the position 
of these closures, together with the nature of the perforations, is 
a character of considerable importance, although it is neither so 
available nor so important as the horny operculum. 
Among, the Paleozoic fossils there is in one or two a structure 
which may represent the suboral pore or avicularium; and as long 
as we do not know the signification of the “adventitious tubules ” 
of Diastopora obelia &c., we may be justified in asking if they may 
not possibly have had an homologous origin. 
No Cyclostomata have avicularia or vibracula, and there does not 
seem to be any structure to in any way take their place. 
The ovicells are of the greatest value, but, unfortunately, are not 
found so frequently as in the other suborders. As yet but very 
few have been described, and with fossils the number known is ex- 
tremely limited; but this to a certain extent arises from their 
having been neglected; for in my collection I have a much greater 
number of fossil ovicells than the total number which have so far 
been described fossil. 
