92 CEYLON MARINE BIOLOGICAL REPORTS. 



What is true of C. nummularia is also true of G. parvula (fig. 43) , which in its mode of growth and 

 occurrence is quite analogous with G. nummularia. 



In the same way as in the series with the ball-shaped branchlets, G. clavifera is a surface form, 

 and the more long-branched uvifera is a deep form ; similarly, in the series with disciform assimilation 

 branchlets, the surface form C. nummularia (fig. 36) has an analogous form in the relatively deep form 

 peltata (figs. 31, 32, 33). The changes in form in the nummularia- peltata series are also quite analogous 

 with those in the davifera-uvifera series. G. peltata has long vertical branches with the side branchlets 

 placed aU round and their flattened assimilation discs obliquely directed upwards (figs. 31, 32, 33), 

 whereas C. nummularia has recumbent axes with assimilation discs on the upper side only (fig. 35). It is 

 evident that with this position the exposure of these branchlets to the light is the most favourable one for 

 vertical axes when they have branchlets aU round them, for horizontal ones when they have them dorsi- 

 ventrally developed. That some transition forms with both radial and dorsiventral axes can be found 

 (fig. 32) will be pointed out by me in the description of the different species. 



Just as ttv»/era was predominantly a deep form, so too this G. peltata is only to be met with deeper 

 down in rock pools and other places not too strongly exposed. 



What applies to the different types of the davifera-uvifera series as far as their advantages and 

 disadvantages are concerned, applies also, of course, to the nummularia-peltata series. Thus we see that 

 between G. peltata and G. uvifera there is a similar ecological convergency to that between G. nummularia and 

 G. clavifera. 



Finally, with regard to G. imhricata and G. Ghemnitzia, the latter, in its organization, mode of 

 growth and occurrence, corresponds exactly withC uvifera. The differences are only of a morphological 

 nature, and only apply to the form of the branclilets, i. e., G. Ghemnitzia (fig. 27) has quite cylindrical 

 branchlets at the base of the vertical axis. G. Ghemnitzia is also, in accordance with its organization, a 

 form which occurs by preference in still water deeper down often together with G. uvifera. 



G.imbricata {figs. 37 — 42), on the other hand, is a species which seems to prefer the upper littoral 

 region. It is as a rule closely tufted (fig. 37), which gives it a certain likeness to G. nummularia. It 

 might be characterized as a G. peltata in which the branches have contracted, so that the vertical axes 

 are very short as are also the branchlets, while they are almost pressed together, thus forming an almost 

 continuous assimilation surface. The detailed description of the species will also show that there are 

 certain transition forms between G. imhricata and G. parvula. 



ThisC imftncato grows on coral reefs together with C. clavifera and G. nummularia, but is far less 

 frequent, and does not occur on strongly exposed parts. So, on the reef at Galle, this species was only to 

 be met with on the more sheltered rocks below the Chppenberg Bastion and the Neptune Bastion. It is 

 evident that the form points to a surface enlargement of the assimilation system, if we compare it with 

 G. nummularia and parvula, since isolated branches grow up vertically and become covered with assimi- 

 lation discs (figs. 41, 42). But this also involves greater danger of laceration, as the strain is increased. 

 It seems, therefore, as if G. imhricata may be conceived as a variant of the nummularia type that has 

 increased its assimilation system, and that occurs where the external circumstances do not stand in its way. 

 (C). — G. sertularioides type. 



It follows from what has been said above that the bilateral Gaulerpa forms in common are to be 

 met with in deeper regions, whereas the radiate forms in general have their main distribution in the 

 littoral region. Certain of the radiate species are replaced in the uppermost Uttoral zone by more or less 

 dorsiventral species. 



It is to be noted, however, that in the Ceylon marine flora a typically bilateral Caulerpa also occurs 

 in the uppermost parts of the littoral region, viz., G. sertularioides (figs. 7-10). I have akeady pointed 

 out above the advantages and disadvantages which are connected with the bilateral shoot form in 

 general, which may be shortly characterized as follows :— the assimilation surface is extended, but this, on 

 the other hand, is accompanied by an increased risk of laceration. As a matter of fact, all the bilateral 



