300 
is the case in the nearly related species 5. intermedia (pl. IV, 
figs. 7—10) in which, however, the lateral teeth are less developed, 
and the adcauline membrane only indistinctly defined from the rest 
of the adecauline wall. I must regard both species as intermediate 
forms between Thujaria and Sertularia, and I cannot doubt but 
that the latter genus has developed from the former by a trans- 
formation. of the distal part of the adcauline wall. 
” Sertularia Suensoni nm. sp. 
(pl. IV, figs. 16—20). 
The colony, the height-of which is 67 mm, has a thin, 
but rather rigid ,geniculate stem, which increases in thickness 
towards the tip, and is divided into distinct internodes, each of which 
bears a branch. The branches, which rise from the stem at 
an angle of about 70?, present a spiral arrangement, the sixth 
being placed over the first. They are regularly and richly dichoto- 
mously branched, each being divided 7 times, and, therefore, they 
form a very dense tuft, which in the colony examined takes up 
the distal half, the branches. in the proximal half being only 
represented by a few proximal internodes. The internodes of the 
branches bear 5—13 hydrothecae. 
The hydrothecae, the length of which is c. 0,5 mm, are alter- 
nate or subalternate, provided with a short free, obliquely ascending, 
not outwardly curved distal end, and divided from each other by 
interspaces which inerease in length towards the end of the branches, 
where they may attain the length of a hydrotheca. The aperture, 
which is turned a little towards the frontal surface of the colony 
and is provided with two large, triangular lateral teeth, has a con 
cave adcauline sinus without a median projeetion, and the adcauline 
membrane, which is not. angularly bent and slopes a little out- 
wards has an almost straight free edge, which meets the corres- 
ponding edge of the abeauline membrane at an angle of .c. 50”. 
In opposition to what is found in the large plurality of Sertularia- 
species the abecauline membrane, therefore, has no free valvular 
