144 
THE VOYAGE OF H.M.S. CHALLENGER. 
Symplegma^ n. gen. 
Colony formed of several ovate heads connected by branched peduncles. 
Ascidiozooids moderately large, not much elongated, and not divided into regions. 
Test firm, vessels numerous. 
Branchial Sac large and well developed, provided with internal longitudinal 
bars. 
Dorsal Lamina in the form of a plain membrane. 
Alimentary and Reproductive Organs forming a mass projecting for a short 
distance behind the branchial sac. 
This genus is formed for a very remarkable species, which, while belonging probably 
to the Distomidse, shows certain characters which are not found elsewhere in that 
family, and on the other hand are characteristic of the Botryllidse. These are the highly 
vascular test (see PL XVIII. figs. 8, 9), the presence of internal longitudinal bars in the 
branchial sac (PL XYIII. figs. 10, 12), the absence of languets on the dorsal lamina 
(PL XVIII. fig. 13), and the want of a well-marked abdomen. In general appearance 
and structure the colony is a Colella (see PL XVIII. fig. 7), and looks not unlike Colella 
concreta and Colella ramtdosa, but the above mentioned characters — especially the struc- 
ture of the branchial sac and of the dorsal lamina — are so remarkable and important that 
it is necessary to form a new genus. There is only one colony in the collection. It was 
obtained in shallow water off Bermuda. 
Symplegma viride, n. sp. (PL XVIII. figs. 7-14). 
The Colony is composed of ovate or elongated masses connected by branched 
peduncles. The head varies greatly in form, but is always narrow at its lower end, 
where it tapers gradually into the top of the peduncle. The colour of the head is a dull 
green with spots of reddish-brown scattered here and there. The peduncle is of a dull 
greyish-yellow colour. The surface is uneven and not smooth. 
The length of the head is 1’2 cm., the greatest thickness is 0’7 cm., the length of 
the peduncle is about 1'5 cm., and its thickness 0'3 cm. 
The Ascidiozooids are fairly large, and are so numerous as to occupy nearly the whole 
surface of the head. They show as ovate projections about 2 mm. in greatest length. 
They are not much elongated antero -posteriorly, and are not placed at right angles to 
the surface, but incline from the anterior end downwards and inwards towards the top of 
the peduncle. 
The Test is small in quantity. It is rather hard and firm, and is not transparent. 
It is of a dull green colour. The matrix is firm and homogeneous, but is penetrated by 
