350 PERCY SLADEN TRUST EXPEDITION. 
The apertures of the dactylopores are either round or top-shaped (figs. 2 & 3) and 
are usually provided with a horseshoe-shaped lip, very similar to that of Distichopora 
profunda. 
The sack in which the gastrozooid lies is remarkably tough in appearance, as described 
by Moseley in S. dichotoma, and sections show that it contracts together near the 
external aperture of the gastropore, so as to completely close it. There are usually four 
short tentacles, as in S'. dichotoma. The dactylozooid also lies ina sack, which, however, 
isnot so tough as that of the gastrozooid. The dactylozooids do not vary so much in size 
as those Moseley described in his species, where the larger might be twice the size of the 
smaller. But a much more important difference is that they bear no axial cavity, such as 
he describes, surrounded by two or three layers of transparent nucleated cells. The axis 
of the dactylozooid is entirely filled up by a solid scalariform endoderm, such as is common 
in the tentacles of other Hydrozoa and such as was described by one of us in Distichopora 
violacea (2. p. 505) as a “ nucleated syncytium with large vacuoles containing probably 
water only.” 
The dactylozooids of all genera of Stylasterina that we have examined (Pliobothrus is 
the only one that we have not seen) have solid endoderm ; it is always vacuolated, though 
not necessarily scalariform in appearance. As in the gastrozooid, there is a well-defined 
muscular layer between ectoderm and endoderm, such as was carefully described by 
Moseley in his species. Another difference that we have observed from the condition 
figured by Moseley is that the zooids, especially the gastrozooids, have living tissue very 
much deeper down the pores than shown in his plate iii., and this we have also found to 
be the case with the gastrozooids of Spinipora, the only other genus that he figured 
which has very deep pores. 
The female ampullee are visible from the exterior in Sporadopora providentie as slight 
swellings; they occur on both surfaces. 
This species may be defined :— 
Hydrophytum flabellate, dichotomous ; zooid-pores scattered, principally at the edges of 
the branches; gastrozooid with four short tentacles. 
The species differs from Sporadopora dichotoma, which was obtained by the ‘ Challenger ’ 
in 600 fms. off Rio de la Plata and which is the only other species of the genus known 
to science, in being more slender in structure, in having the greater number of the pores 
on the edges of the branches and arranged there in rows as in Distichopora, and in the 
absence of a cavity in the dactylozooids. In all these characters it shows affinities with 
the genus Distichopora and more particularly with the species D. profunda. It is of 
some interest that in the series beginning with D. violacea from shallow water, D. profunda 
from 120-150 fathoms, S. providentie from the same depth, and §. dichotoma from 600 
fathoms we have aseries connecting the two genera. The conclusion may be either that 
Sporadopora is a genus derived from Distichopora and adapted toa deep-sea habit, or the 
reverse; but, of course, the evidence in favour of either of these conclusions requires 
considerable strengthening to be placed on a firm footing. 
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