17 



sure-plate. As a rule this closure begins with the formation of three slender pro- 

 cesses (pi. II, fig. 9) starting one from the end of the new aperture and the two 

 others from the lateral margins of the old one. They unite about half the way 

 between the end of the new and that of the old aperture, and the three open spaces 

 are later filled, each by a calcareous lamina. A similar closure also takes place 

 when a new zooecium is regenerated within a large heterozoaecium (pi. II, fig. 5). In 

 the Cyclostomata a complete regeneration seems to be very rare, and I have hitherto 

 only been able to find a few indistinct cases in Entalophora madreporacea and 

 Homera lichenoides. 



The Closure. 



The closure of old zooecia by means of a calcareous film is a well-known fact 

 both in the Cheilostomata and the Cyclostomata, and it seems to be more common 

 in the latter than in the former division. The real operculum of the Melicerititidce, 

 which has been correctly interpreted by d'Orbigny has by all later authors been 

 regarded as a closure-plate, and with the exception of Waters who mentions a 

 peculiar form of closure in Meliceritites Royana no author seems to have noticed a 

 real closure in this division. I have found a closure in almost all the species 

 examined, not only in the zooecia, but also in the heterozooecia, and as a rule the 

 zooecia are closed by a concave or sometimes flat calcareous film (pi. I, figs. 4, 14, 

 1(5; pi. II, fig. 7; pi. Ill, figs. 7, 26; pi. IV, figs. 6, 7, 15; pi. V, figs. 2, 19; pi. VI, figs. 

 4, 10), which in the species provided with an oral ledge either starts from the 

 inner margin of the latter or at a somewhat deeper level; and in that case the 

 aperture is lastly closed in its proximal and middle part (pi. II, fig. 7; pi. Ill, fig 

 25). In the other species the closure starts from the margin of the aperture and 

 gradually extends towards the centre (pi. IV, fig. 15). In Mel. magnifica (pi. I, fig. 

 7) and Mel. plana d'Orb. (pi. V, fig. 12) the closure takes place by means of 3 — 5 pro- 

 cesses starting from the margin of the aperture and later coalescing into a cover 

 perforated by 3 — 5 holes, which are gradually closed. A third form of closure I 

 have found in Mel. palpehrosa (pi. VII, fig. 1, 4 — 9). In opposition to what is found 

 in the operculum the closure-plate never presents a flabelliform striation. 



The Colonies. 



In opposition to the rich diversity of colonial forms or forms of growth shown 

 by the Cyclostomata the number of colonial forms presented by the Melicerititidae 

 is very small, and we can only discern between incrustihg disciform colonies, one-or 

 two-layered laminose fronds, and ramose colonies with cylindrical branches. The 

 laminose colonies sometimes form hollow expansions f. inst. in Mel. Vieilbanci or 

 a reticulate network, f. inst. in Retelea pulchella d'Orb. In many species the colo- 



U. K I) Viilensk.Selsk.SUr., 7. Rickke, naluivideiisk. og iiKitheni. Alii X. 1. 3 



