378 P* Kramp. 



polysymmetrical and can be closed by an operculum, and the gono- 

 thecae of which are attached singly, not in aggregates. — hi Stego- 

 poma we have only two planes of symmetry, in Tetrapoma four planes, 

 in the other genera more. — All other operculated hydroids are 

 bilaterally symmetrical and have only one plane of symmetry; this 

 is a very important characteristic for the whole family Serhilaridae; 

 on the other hand, the bilateral form in Toichopoma, the only oper- 

 culated genus among the Lafoëidae, is of less systematic importance. 

 Nor is it this character which distinguishes Toichopoma from the 

 Campamilinidae, but the possession of a "Coppinia". 



The structure of the operculum in the Campamilinidae has been 

 but little investigated and has been misunderstood in several ways. 

 — The pyramidal operculum was considered for a long time to 

 consist of free, triangular valves (see e. g. Hincks (28) PI. 38). A more 

 correct view was first given in 1892 in the two papers of Levinsen 

 (87) and (38). Levinsen described the different forms of operculum 

 and divided the genus Calycella into 4 genera: Cahjcella, Tetrapoma, 

 Stegopoma and Toichopoma. Of these Toichopoma is mentioned among 

 the Lafoëidae; to the descriptions of Stegopoma and Tetrapoma there 

 is nothing to add. With regard to the many-sided opercula (with 

 more than four facets) Levinsen has shown, that they close by 

 folding, except in Lovenella where the operculum consists of free 

 valves. I have not investigated Lovenella myself and have no opinion, 

 as to how far it is correct of Broch to include this genus with 

 Tetrapoma. — In the other genera Levinsen described the operculum 

 as consisting of triangular facets, between which there are thinner, 

 chitinous parts, which on closing are folded inwards and are more 

 or less apt to split. 



Levinsen's view of the development of these opercula was as 

 follows. The young hydrotheca is closed by a roof; in this appears 

 at a certain time a number of radiating lines, which do not reach in 

 to the centre of the roof; when the full-grown hydranth pushes out, 

 the central part of the roof will be thrown off, and the remainder will 

 become the above-described operculum. Levinsen certainly under- 

 stood, that in Cnspidella, Lafoèina, Opercnlarella and Campanulina, 

 the operculum is not marked off from the calycle by any edge ((38) 

 p. 176); but this means, that in the genera mentioned the roof of 

 the hydrotheca is not sisparated from the calycle by any edge, 

 in this sense we can understand the emphasized sentence ((37) 

 p. 16): "I alle Tilfælde opstaar Laaget ved en Omdannelse af Ну- 

 drothekets oprindelige Tag", that is, in all hydroids except Toicho- 

 poma and Stegopoma the operculum arises by a transformation of 

 the original roof of the hydrotheca. hi fact, the roof in the Campanuli- 



