360 J. E. Durrpen—Jamaican Actiniaria: Part I.—Zoanthee. 
Form.—Polyps smooth, rigid, cylindrical, arranged in a somewhat rectangular 
manner; the smooth ectoderm is easily rubbed off exposing the mesoglea below, 
with a roughened surface due to the foreign incrustations; in retraction rounded 
or somewhat flattened above, free for a short distance beyond the surface of the 
ccenenchyme. In the living state, or when preserved in formalin without con- 
traction, the polyps are equally free all round, and so closely arranged that they 
are separated above only by polygonal dividing lines, none of the ccenenchyme 
being visible (fig. 7). Specimens which have been preserved in alcohol and in 
which shrinkage has taken place are not equally free on all sides, but con- 
nected with one another by four (may be three or five when the polyps are 
not arranged in a rectangular manner) higher, occasionally grooved, ridges of 
ccenenchyme, and rounded depressions of ccenenchyme, are seen in the spaces 
between (fig. 8). A central, slightly depressed aperture remains in retracted 
polyps, and occasionally three to six longitudinal wrinklings along the free portion 
of the wall of the peripheral polyps are present in specimens preserved in alcohol, 
and also transverse wrinklings. The amount of the free portion varies according 
to the state of extension or retraction of the polyps in a colony. Usually in 
complete retraction about 04cm. are free; in partial retraction, when the full 
capitular ridges can be counted, and in full expansion, about 0-6 em. are free. 
In almost complete retraction the capitular ridges are wedge-shaped with very 
narrow furrows; as the polyps slowly open, the ridges become more convoluted or 
laterally undulating, and finally appear as so many acute marginal denticulations. 
These, as already shown above, are usually from 18 to 20 in number. The 
polyps of three other colonies from South Cay had a very regular number of 
ridges as follows :— 
A.—19, 18, 18, 18, 18, 18, 18, 19, 18. 
B.—19, 18, 18, 18, 18, 18, 18, 18, 19, 18, 19, 18, 19. 
C.—18, 21, 18,19, 18, 18, 18. 
Tentacles very short, smooth, acuminate, dicyclic, inner row opposite the mar- 
ginal denticulations, slightly entacmzous, overhanging in extension, 18 to 20 in 
each row. Disc cup-shaped in partial, and saucer-shaped in full, extension, but 
with the central part appearing as a dome and bearing the slit-like mouth at the 
apex. The peripheral zone of the disc is thin-walled, pellucid, smooth, devoid ot 
incrustations, and raised into elevations and grooves corresponding with the 
number of tentacles, of which it appears as a continuation. In full extension it 
is flat or may be arched over; in partial extension it is nearly vertical. The 
central part of the dise is smooth, but contains a few incrustations. The species 
usually occurs in small, rather high colonies, closely associated with one another, 
but separated by deep channels. The incrusting base is much smaller in area 
than the distal surface, the peripheral polyps being arranged obliquely or 
