8 
By such a splitting of a colouy in singular rows of zooecia eacii 
lateral rosette-plate is divided in two very different parts, namely 
in a watch-glass-formed chief-part, whose convexity faces inwards, and 
in an annular marginal part belonging to tlie side-wall of the neigh- 
bouring zooecium. Althongh both parts together constitute the 
whole rosette-plate, we will for simplicitys sake in the following 
exposition call the chief-part the rosette-plate and the annular 
part the hole. When the zooecia according to the general rule 
are disposed in the so-called quincunx-position, namely in such a 
manner that the zooecia in two neighbouring rows are alternating, 
the anterior half of each lateral wall shows a number of rosette- 
plates and the posterior half a number of holes corresponding with 
as many rosette-plates in the anterior half of a neighbouring zooe¬ 
cium ‘). On the contrary, if two zooecia are contiguous in their 
whole length, each lateral wall will show either rosette-plates or 
holes. A singular exception to this rule makes Electra pilosa, for 
although this species as a rule shows the regular quincunx-position, 
the lateral walls through a whole row of zooecia in the same side 
are provided either with rosette-plates or with holes. In many 
cases (for instance in Memhranipora Dumerilii, CribriUna punctata, 
Diazeuxia hyalina, Mucronella coccinea etc.) the rosette-plates have 
their place in the inner wall of small additional structures from the 
zooecia for which I have earlier proposed the name of pore-cham- 
bers ^). The basal wall in 'such a pore-chamber is continuous with 
that of the zooecium, whereas the outer wall in which the entrance 
to the chamber is situated forms an acute angle with the basal 
wall. Like the watch-glass-formed chief-parts of the rosette-plates 
the pore-chambers are as a rule only to be found in the anterior 
half of a zooecium, and the posterior half, in which the walls form 
obtuse angles with the basal wall, is provided with holes corre- 
G. M. R. Levinsen Mosdyr, Zoologia danica, 9. Hefte, 1894. pag. 8, 
Tab. I—IV. 
G. M. R. Levinsen, Op. cit., pag. 7, Tab. IV—V. 
