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of Hincks, and others, the type of his genus Amphiblestrwm Gray, and he 
_ places in the group six species, four of which are described and figured 
ON RECENT POLYZOA. 485 
in the report, the other two referred to and redescribed. The trifoliate 
character of the orifice is not found in the whole of Mr. Busk’s species ; 
some orifices are obovate, but all have a partially internal calcareous 
lamina. So that in dealing with the two groups—Megapora and Amphi- 
blestrum—we shall have to deal with other characters besides that of the 
trifoliate orifice. In all probability the one or the other peculiarities of 
the group date back to the Upper Chalk, but in a very modified form as 
regards species. 
In the Microporipz the front wall of the zocecia is wholly calcareous, 
but the margins are elevated and there is a slight tendency to trifolation 
in M. complanata, but there are no marginal spines. In his papers on 
Australian Bryozoa Mr. Waters places two or three forms in this genus, 
and he alludes to one form as M. hippocrepus, Goldf. None of the species, 
however, are to be compared with the semitrifoliate orifice of M. com- 
planata, Norman=Membranipora Smitti, Manzoni. We thus carry back 
the partially trifoliate orifice to the Italian Pliocene, but we also find it, 
together with other characters, in Membranipora trifolium in the Crag. 
In Steganoporella there is in the orifices of some of the cells a slight 
tendency to trifoliation; but there are other marked characters which 
separate the species from Micropora, although the external aspect of forms 
of the two genera are similar. Only one species is described by Mr. 
Hincks, 8. Smittii, but in describing S. magnilabris, Busk, Chal. Rep., Mr. 
Busk re-defines and limits the genus and species. ‘The chief character 
on which the genus Steganoporella, Hincks,... . is based is the 
bithalamic condition of the zocecium. Some way below the upper ex- 
tremity of the cell a diaphragm shuts off the lower portion of the cavity, 
and forms a distinct chamber for the polypide. A tubular passage extends 
upwards from this chamber, and opens . . . . into the upper chamber, 
which is always large, and in certain cells of very ample dimensions .. . . 
The opening of this chamber is closed by a very large operculum... . 
which also protects the entrance to the tubular passage through which 
the polypide issues.’ (Hincks’ ‘ Annals,’ Feb. 1882, p. 83.) ‘ Smitt places 
Steganoporella amongst the Microporide . . . . but Iam now inclined to 
agree with Dr. J. Jullien so far as to regard the dithalamic condition of 
the zocecium, which distinguishes it, as entitling it to rank in a separate 
family group’—Fam. Steganoporellide, Hincks. (Annals, May, 1884, 
p. 358.) Ihave preferred to give, on this point especially, both the first- 
formed and matured expressions of the author. 
Another very important group which seems to be far more natural 
that the last is the Myrizoma, Smithand Hincks. It contains the genera 
Schizoporella, and Mastigophora, of Hincks, and its distinguishing feature 
is the sinus on the lower margin of the orifice. The sinus is also found 
in species of Hippothoa which Mr. Hincks places in the family, but not- 
withstanding this Mr. Busk (Chal. Rep.) removes it and places it with 
his stoloniferous group, particulars of which are given in the body of the 
present report. But as in other groups, so in this, dependence in the 
divisions must not be placed upon one character alone; other characters 
must be considered as well as this, and the systemist would do well to 
look all around his species before deciding to which group it belongs. 
The sinus of Schizoporella spinifera is very much like the sinus of Smittia 
marmorea ; so also is the orifice, excepting the spines in the former species. 
