SUMMARY AND GENERAL REMARKS. 
The present section will consist of a brief summary of the chief additions made by 
the Challenger Expedition to our knowledge of the Compound x^scidians, along with a 
discussion, where necessary, of any structural points of interest or novelty. An account 
of the probable phylogeny of the group, and of its relations to the other Tunicata, 
wHl conclude this part of the Eeport. The remarks upon the different genera and 
species in the following pages are arranged in the same order in which the families 
were treated in the preceding systematic part of the work, beginning with flie Botryllidae 
and ending with the Polystyelidae. This, as was pointed out in the Introduction, is 
a somewhat artificial arrangement. The natural relations of the families will be discussed 
further on, in connection with the phylogeny of the group. 
The family BotryUidse is represented in the collections by seven species and a well- 
marked variety, all new to science. It is remarkable that all the Challenger specimens 
belong to the genus Botrylloides, while Botryllus, which is so common on the coasts of 
north-west Europe, was not obtained in any of the expeditions. The Botryllidue were 
all collected to the north of the equator, and the only tropical region in which 
they occurred was the Philippine Islands. No new genus has been required in this 
family. The name of the new species described on page 41 as Botrylloides purpureum 
I now change to Botrylloides tyreum, as the specific name purpureum was pre-occupied 
by a distinct species.^ 
The family Distomidse is represented by fifteen species and a well-marked variety. 
It is a large group, including von Drasche’s family Chondrostachyidse, and a series of new 
forms, for which the genus Colella has been founded (see p. 72). This genus is allied to 
Distaplia, Della Valle, and to Oxycorynia, von Drasche ; it contains nine species and a 
variety, all new to science with the exception of Colella pedunculata, described in 1834 
under the name of Aplidium pedunculatum by Quoy and Gaimard. Most of these forms 
have the test of the lower part of the colony remarkably modified, so as to form a well- 
1 See von Drasche, Die Synascidien, p. 15. 
