21 



lamina. A second form of closure is that pointed out by Waters. It starts by the 

 growing forth from the margin of the aperture of 2 — 5 processes which later coa- 

 lesce after which the smaller ai)ertures between the processes are gradually filled 

 out. Both forms of closure may be found in the same colony, but as a rule one 

 of them is predominant. 



The heterozooecia are closed by a filling out of the two fissures found in the 

 opercular cover. — 



The Ooecia are of very different form and size. 

 Kenozooecia have not been found. 



Regeneration is found both of the zooecia and of the heterozooecia, but with 

 the exception of a few indistinct cases always in that manner that old zooecia have 

 been regenerated by new zooecia and old heterozooecia by new heterozooecia. There 

 has be seen as many as three regenerations in a single zooecium or heterozooecium. 

 The Colonies are erect with cylindrical branches, and when old are surrounded 

 by a number of superficial layers of new zooecia, which may arise in very different 

 parts of the branches. The zooecia and heterozooecia show a disposition to arrange 

 themselves in transvers series in such a manner that two series of zooecia are fol- 

 lowed by a single series of heterozooecia, and in the most regular colonies these 

 series form more or less complete, more or less unmixed, ringshaped bells sur- 

 rounding the branches. Sometimes, however, the arrangement of the zooecia and 

 heterozooecia may be more or less irregular, and the heterozooecia may sometimes 

 be present in sparse numbers, irregularly distributed among the zooecia (var. royana 

 Wat.). The zooecia placed between the distal halves of the heterozooecia are pro- 

 vided with a small narrow subopercular area, while in the other series of zooecia 

 the subopercular area is as a rule much broader, but the proximal part of it is 

 concealed by the distal end of the proximal heterozooecia. 



Critical remarks. In d'Orbigny's figure 2 is seen distally to each transverse series 

 of heterozooecia a transverse series of zooecia which differ from those placed pro- 

 ximally to the heterozooecia by the possession of a very small half-elliptical aper- 

 ture. The zooecia of this series, however, do not differ from the other in the form 

 of the aperture, and d'Orbigny's error musl no doubt be explained in that way 

 that he has seen in such a series a number of regenerated zooecia (see pi. 1, fig. 3), 

 the structure of which he has misunderstood. For the rest d'Orbigny regards the 

 heterozooecia as »cellules ordinaires« and the zooecia as »cellules accessoires«. — 

 In longitudinal sections of many-layered colonies of this species Waters means to 

 have seen that the zooecia of the external layers arise from a plate covering the 

 aperture of the subjacent zooecia. I do not agree with Waters in that question, 

 and to my opinion a longitudinal section of such a colony only shows that the 

 inner wall of the external zooecia has quite coalesced with the frontal wall of the 

 subjacent ones. That the operculum or the closing plate of an old zooecium should 

 be able to give rise to a new zooecium is not very probable, and that each zooecium 

 of the external layer should grow forth from a subjacent one does not correspond 



