180 
~ 
the characters of the peristomes are not in all cases of value for 
purposes of discrimination of species. In the present species, 
for instance, the tubes have either their ostia flush with the 
surface, or else they project a little from the surface. When, 
however, as in the piece of tubarium shown in fig. 11, the 
branch is growing so rapidly that the intervals between the 
tubes have not been filled up by common test, the tubes stand 
out boldly, and one would have to apply to such a piece the 
expression “* peristomes Jong.” This condition is exceptional, 
it is true, and would probably have been of short duration, 
but it indicates a difficulty in the satisfactory employment of 
the characters of the peristomes for distinguishing one species 
of Cephalodiscus from another. 
In the piece of the colony shown in fig. 11 the spine c is, I 
take it, older than any of the three tubes shown, and was 
originated by a polypide whose tube does not appear in the 
piece selected, being set lower down the branch. The polypide 
occupying the tube 6 utilised this spine as a support for its tube, 
and originated from the side of the spine two spines of its own, 
d and e, the latter only in the initial stages of its formation. 
The polypide of tube a started a spine of its own (f), with its 
base against the side of the tube; and the polypide of the tube 
g produced two spines, one (/) set upon the side of the spine c, 
and the other (7) originating from the side of the tube. 
Polypides.—The polypides of Cephalodiscus gilchristi do not 
present any remarkable peculiarities. The shield has a dark 
band around its front and side edges (fig. 4, plate 2, b.s.) which 
is peculiar to the species, but the red line (7./.) and other fea- 
tures do not call for special comment. The shield is a very 
mobile organ judging from the numerous shapes in which it 
is found in the preserved material ; and in buds especially is 
the posterior flap found either directed backward ventral to 
the mouth and parallel to the post-oral lamella (fig. 5, plate 
2), or turned forward so as to be ventral to the main portion 
of the shield (fig. 6), or set at any angle intermediate between 
these two extremes. 
The twelve plumes stand out rather distinctly in well- 
preserved polypides, and the ends of the individual plumes 
appear more pointed (fig. 4, plate 2. fl.) and less bunched than 
those of C. dodecalophus and C. hodgsont, which they otherwise 
most nearly resemble. The body is swollen, the posterior end 
moderately pointed when seen from the ventral or dorsal 
aspect. The stomach causes a bulging of the two sides of the 
body (ga.); and in front of these projections there are in 
mature polypides a pair of others (go.), due to the gonads. 
The course of the rectum can usually be traced as a shallow 
