384 
THE VOYAGE OP H.M.S. CHALLENGER. 
The family Didemnidse is represented by nineteen species and at least four varieties. 
One of the species [Leptoclinum alhidum) was previously known, the other forms are all 
new to science. Nearly aU of these species are opaque white or grey; a few, however, are 
pigmented. Didemnum savignii is a chocolate-brown, Didemnum aurantiacum is 
orange, and Leptoclinum ruhicundum is of a rust red colour. The Didemnidse have a 
world- wide distribution. 
Some of the Challenger species of Leptoclinum form remarkably calcareous colonies, 
the spicules being very numerous and densely crowded in the test (see Leptoclinum 
moseleyi, p. 272). The relation of these calcareous spicules to the test matrix and cells 
is discussed in the case of Leptoclinum tonga (p. 269). 
Two new species belonging to the interesting family Diplosomidse were obtained 
during the Challenger Expedition. For one of them, along with a previously described 
species of von Drasche’s {Diplosoma pseudoleptoclinum) , I have founded the new genus 
Diplosomoides. 
Probably the single colony of Coelocormus huxleyi, which was obtained from a depth of 
600 fathoms off the east coast of South America, is the most remarkable and important 
Compound Ascidian in the collection. It is an unattached massive colony, with an axial 
cavity. The branchial apertures of the Ascidiozooids are five-lobed, a condition not 
found in any other Ascidians. There are a few calcareous spicules in the upper layer of 
the colony, like those of the Didemnidse ; and the male reproductive organs are in an 
intermediate condition between those of the Distomidse and of the Didemnidse. On 
account of these and other remarkable peculiarities (see p. 317), I have found it necessary 
to establish a new family, the Coelocormidse, occupying an intermediate position between 
the Diplosomidse and the Pyrosomidse (see also under Phylogeny, p. 394). 
The Polystyelidse, a group which I have raised to the rank of a family, has important 
relations with the Cynthiidse amongst Simple Ascidians (see under Phylogeny, p. 398), 
and is well represented in the Challenger collection. This family was only known 
previously from a few species obtained on the shores of north-west Europe, and a single 
species [Goodsiria coccinea) from the Strait of Magellan. To these the Challenger 
investigations have added four new species and a variety. 
One new genus has been formed for Chorizocormus reticulatus, a species from 
Kerguelen Island which exhibits particularly well the gradual union of Ascidiozooids 
to form a colony (see p. 346). 
The relations of this family to the Simple Ascidians on the one hand, and to the 
Botryllidse on the other, are discussed in connection with the phylogeny of the Compound 
Ascidians further on (p. 398). 
The new Challenger Polystyelidse are nearly all from southern latitudes. Some of 
them form very large colonies, and the Ascidiozooids are much larger than in the case of 
most Compound Ascidians. 
