A. W. WATERS—REPORT ON THE BRYOZOA,. 161 
structure was the same, and also that there was no relationship with 
Schizoporella *. 
The species of Holoporella known from the tropics are H. aspera (Busk) ; 
LH. albirostris (Sm.); H. aperta (Hincks); H. columnaris (Busk); H. discoidea 
(Busk), and var. frutetosa, Kirkp.; H. fusca (Busk) ; H. granulosa (Hasw.) ; 
Hf, fossa (Hasw.) ; H. imbellis (Busk) ; H. lewis (Hasw.) ; H. mamillata 
(Busk) ; H. speciosa (MacG.); H. simplea (MacG.) ; H. tridenticulata (Busk) ; 
HT. samboangensis (Busk) ; H. turrita(Sm.) ; H. Descostilsi (Aud.); H. vermi- 
formis, nov. ; H. pigmentaria, nov. 
The diagnosis of Monoporella, Hincks, would apply to Holoporella, but 
H. nodulifera and H. lepida could not be united to Holoporella, so that a 
fuller diagnosis of Monoporella is required, as it is probably a good genus. 
HoLopoRELLA APERTA (Hincks). (Plate 18. figs. 20-23.) 
Schizoporella aperta, Hincks, Ann. Mag. Nat. Hist. ser. 5, vol. ix. (1882) p. 89, pl. 5. 
fiz, 3; op. cit. ser. 6, vol. xi. p. 176 (1893); Thornely, “ Manaar,” p. 114 (1905); Rec. of 
Indian Museum, vol. i. pt. 3, no. 13 (1907) p. 189. 
Monoporella albicans, Hincks, Ann. Mag. Nat. Hist. ser. 5, vol. ix. (1882) p. 86, pl. 5. 
fies. 5a, b; Waters, op. cit. ser. 7, vol. xv. p. 16; Thornely, “ Manaar,” p. 113 (1905). 
Cellepora brunnea, Hincks, Ann. Mag. Nat. Hist. ser. 5, vol. xiii. (1884) p. 80; Journ. 
Linn. Soc., Zool. vol. xxi. (1887) p. 182. 
* As the examination of the opercula has so largely assisted in establishing this genus, it 
may be well for a moment to consider why it is, that the operculum furnishes such useful 
characters in classification, in fact far away the most useful. When in my paper “ On the 
use of the Opercula, &c.” (Proc. Manchester Lit. & Phil. Soc. vol. xviii. p. 8, pl. i., 1878), 
I first showed how they might be used, it was principally as indicating the shape ofthe 
oral aperture, which it is often difficult or impossible to examine, for the peristome may 
hide the aperture, or it may even be well inside the zowcium, directed towards the distal 
end. In nearly all cases the amount of individual variation is extremely small, so that in 
a slide of 50 opercula there may be no apparent variation. The importance of noticing the 
position of the muscular attachment was alluded to, and this is a point that extended 
examination shows is of the first importance. 
The operculum as it must now be studied, however, shows not only the size and shape 
of the aperture, but also the position of the muscles in the zocecium ; and it is influenced 
by the compensation-chamber, by whether it has to close the ovicell, and by the way in 
which the tentacular sheath is attached. The operculum is nearly always hinged to teeth 
or condyles at each side, and these are often indicated on the opercula, and, further, from 
the operculum grows the tentacle-sheath for the new bud. Thus the operculum alone bears 
the impress of many important zocecial characters. 
The mandibles also furnish some characters, but are extremely variable in size and are 
subject to great modifications, and we must not expect them to give as valuable information 
as the opercula. The positions of the muscles, lucida, and columella are, however, useful. 
I may add that many species can be determined by means of decalcified sections alone, 
and as the anatomy is more studied it will be possible to determine a larger number in 
this way. 
