112 CATALOGUE OF THE ZOOniYTES OF 



Without a careful examination of its characters, this species 

 might be passed over as a smaller variety of S. polyzonias, from 

 which it differs in the slenderness of its proportions, in the shape 

 of the cells, and especially in their three-toothed apertures. Mr. 

 Busk has pointed out to me that there is a species very much 

 resembling this found in the South Seas (the S. Jolinstoni of 

 Gray), of which he has kindly sent me a specimen from New 

 Zealand. Like our species, it is tridentate ; but on a careful com- 

 parison of the two, I find that the southern form differs from ours 

 in the following particulars. It is of smaller size and more com- 

 pact mode of growth; the cells are more closely set, smaller, 

 shorter, broader at the base, and attached for a greater part of 

 their length, besides having some peculiar rib-like thickenings of 

 the walls that are not found in the northern species. There are 

 likewise occasionally two or three cells together without a joint. 

 The ovicapsules are very similar, but the aperture is not so much 

 produced, and is conical, not funnel-shaped. 



S. tricuspidata is parasitical on other zoophytes, adhering to 

 them by a creeping, much-twisted fibre, from which stems arise 

 at intervals to the height of one or two inches. They are slen- 

 der, pale horn-coloured, rather shining, dividing dichotomously, 

 or giving off alternate branches, which are frequently again sub- 

 divided. The branches are much constricted and more or less 

 spirally twisted at their base; there is also a joint and oblique 

 twist above each cell. The stem, after rising a little, occasionally 

 lays hold of another branch of the sujiporting coralline, and be- 

 comes again creeping for a short distance. The cells are rather 

 distant, cylindrical (not bulging below as in S. polyzonias), longer 

 than broad, smooth, attached for about a fourth part of their 

 length, slightly curved outwards and expanded a little at the 

 aperture, which is strongly tridentate, appearing triangular when 

 looked at from above : the margin is thickened by a rib. The 

 ovicapsules are rather more cylindrical than those of S. polyzo- 

 nias, more strongly ribbed across, and have a very narrow funnel- 

 shaped aperture, without teeth. 



Esper's Sertular. Tab. xii., called Sertidaria ericoides, Pall., 

 seems to represent this species. 



