Report on the Hydroids. 379 



nidae is already distinct from the calycle at an early stage in deл'el- 

 opment, and we shall see later, that the roof in Cuspidella etc. does 

 not take part in the formation of the operculum. 



No other view of the operculum in the Campaimlinidae has 

 appeared, so far as I know (I exclude Schneider's criticism (51)), until 

 Broch published his paper in 1909 (17). Broch maintains, that the 

 operculum in all Campanulinidae is formed by the upper part of the 

 lateral wall of the liydrotheca, but for the rest he retains the trian- 

 gular facets. Broch sets up, — as an hypothesis I admit — the 

 following phylogenetic series : Lafoën, Toichopoma, Stegopoma, Cuspi- 

 della^ (the thin parts between the facets do not split), Campanulina 

 and CalijceUa (the thin parts split more or less), Tetrapoma"^ and 

 Louenella (the thin parts present in early stages, but completely 

 fall off). 



As almost all these genera are represented in the material of the 

 Danmark Expedition, I have undertaken an investigation, with the 

 following results. 



Cuspidella. — On examining a fully developed liydrotheca of 

 Cuspidella with closed operculum, we notice that the operculum is 

 not usually separated by any edge from the liydrotheca (PL XXIV, 

 fig. 2); yet a distinct edge can be present, though seldom (PI. XXIV, 

 fig. 6), and this fact has induced Broch to unite Cuspidella and 

 Campanuliua with Calijcella; in the last the operculum is always 

 marked о1Г from the lateral walls of the liydrotheca by a sharp edge. 

 — If we press on the operculum of a Cuspidella and open it (PI. XXIV, 

 fig. 5), we will see that it is a direct continuation of the hydrothecal 

 wall, that the opened aperture is circular and of the same diameter 

 as the liydrotheca, and that the aperture-rim is complete ; if there 

 was a distinct edge between the operculum and the calycle before, 

 this edge will now show itself as a quite faint line. Triangular 

 facets are sought for in Aain; on the other hand, a few lines will 

 be seen, which begin at about the same height on the hydrothecal 

 wall and run parallel up towards the rim of the aperture; before 

 reaching this, they bifurcate but the two prongs do not diverge 

 greatly, the part between is complete and its free margin enters into 

 the formation of the above mentioned unbroken rim of the aperture. 

 By means of these parts the "facets" with their broad ends can 

 fold over one another, so that the closed operculum becomes conical. 

 There is not the slightest doubt, that the operculum in Cuspidella is 

 a direct continuation of the hydrothecal wall, and has arisen by a 



^ Cuspidella, Campanulina, Opercularella and Calycella are united under the 



name Campanulina. 

 ^ Tetrapoma and Lovenella are united under the name Lovenella. 



