8 
body to contain 18*60% of sulpliur, whilst (C 6 H 3 NH 2 ) 2 
requires 18*40% S. 
“The Use of the Opercula in the Determination of the 
Cheilostomatous Bryozoa,” by Arthur Wm. Waters, 
F.G.S. 
In the determination of the Bryozoa various authors have 
attached very different importance to the characters used, 
but the form of the aperture has been recognised by all to 
be of use. D’Orbigny rightly used this very largely, and 
Hassall pointed out that it was much less varying than 
many points. Busk of course mentions the form in most 
cases, but Professor F. A. Smitt, the first authority on the 
Bryozoa, has used it much more largely, and has based his 
classification of the Lepralia and allied genera principally 
upon the form of the aperture. Dr. Hincks also has re- 
cently proposed a new classification in many points similar 
to Smitt’s, in which the form of the aperture is largely made 
the basis. 
It seemed to me that as the shape ot the oral-aperture 
can only indicate the form of the operculum, which closes 
it, the opercula themselves might furnish more reliable in- 
formation, and I therefore prepared a series from the 
material I had available, and I find it may be even more 
useful than I at all expected. Besides indicating the form 
of the aperture, there are also many other characters shown, 
so that in the first 35 examined and figured all have an 
easily distinguishable operculum. 
The operculum is closed by means of two muscles, which 
in some cases, as Myriozoum truncatum, fig. 15 ; Lepralia 
pertusa var., fig. 4 ; Lepralia arrogata, fig. 6, &c., &c., are 
attached at the side, in some quite from the edge, in others, 
as Cellepora, fig. 8, from a muscular boss on the rim ; but 
in most of the Celleporidse, and some Lepralia, &c., the 
muscular attachment is on the interior surface as in Lep- 
ralia Cecilii, fig. 1 ; Cellepora, fig. 5, &c. 
