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EXPLANATION OF THE PLATES: 
PATE, X- 
Photographic reproduction of a colony of Cephalodiscus (Idiothecia) gil- 
christt ; natural size. Specimen No. 18551. 
Pram y2e 
Fig. 1. A branch of the tubarium of Cephalodiscus gilchristi, enlarged 24 
diameters. Specimen No. 13203. 
Fig. 2. Longitudinal section of a branch of C. gilchvisti, enlarged 2} dia- 
meters. The darkest parts are tubes seen in section ; the paler tubes are not 
cut into, but are seen through the transparent test. 
Fig. 3. Transverse section of a branch of C. gilchristi, enlarged 24 diameters. 
Fig. 4. Polypide of C. gilchristt, ventral view, enlarged about 45 diameters. 
b. and b., buds; b.s., dark edge of the buccal shield; ga., bulging of the side 
of the body caused by the stomach ; go., bulging of the side of the body caused 
by the gonad ; p/., plumes ; #.s., posterior lobe of the buccal shield ; ¢./., red 
line of the buccal shield ; s¢., stolon. 
Figs. 5 and 6. Two buds, of about the same age, showing the extremes of 
the positions in which the posterior lobe of the buccal shield may be found. 
a. and p., anterior and posterior lobes of the buccal shield ; b., “‘ body ”’ of the 
bud; s., stalk. 
(Figs. 1-3 were drawn by Miss G. M. Woodward.) 
PEATE Ss: 
Fig. 7. End view of a branch of C. gilchristi showing the relation of spines to 
ostia. Enlarged 44 diameters. At a and at 6 there is one spine between two 
ostia ; each of the other six ostia has a spine of its own. 
Fig. 8. Transverse section of one of the solid cross-bars that connect up the 
branches of the tubarium. Enlarged 6 diameters. a, b, c, d, sections of spines 
buried in the common test. 
Figs. 9, 10 and 11. Terminal portions of branches, to show the relation of the 
spines to the tubes. The spines are all represented as cut short. The irregu- 
lar line in the lower part of figs. 9 and 10 marks where the piece of tubarium 
figured was torn away from the rest of the branch. In fig. 11 the torn surface, 
bounded by the line k, is directed obliquely towards the observer. The figures 
are enlarged 8 or 9 diameters. For explanation of the letters see text. 
