878 
THE VOYAGE OP H.M.S. CHALLENGEK. 
IV. — Between 250 fathoms and 500 fathoms four species were found, viz.: — 
Sarcobotrylloides wyvillii. 
Polycyclus lamarcki. 
[f) clava. 
Cystodytes draschii. 
In this list four genera and two families are represented. 
V. — Between 500 fathoms and 1000 fathoms seven species were found, viz.: — 
Botrylloides fulgurale. 
Polyclinum molle. 
Aplidium incrustans. 
Psammaplidium effrenatum. 
„ Jiavum. 
Leptoclinum tenue. 
Ccelocormus huxleyi. 
In this list six genera and four families are represented. 
VI. — Between 1000 fathoms and 2000 fathoms one species was found, viz.: — 
Pharyngodictyon mirahile. 
From these lists it appears that Compound Ascidians, like Simple Ascidians, are much 
more common in shallow than in deep water, that only eight species extend into the 
abyssal zone, only one species to depths over 1000 fathoms, and that more than half the 
total number of species are found living at depths between 1 and 50 fathoms. 
These lists, however, do not accurately represnt ethe whole state of affairs, as they 
do not take into account the greater facilities for collecting in shallow water, nor yet the 
relative numbers of the deep and the shallow water dredgings performed during the 
voyage. 
Hence the following list, showing the number of dredgings taken by the Challenger 
Expedition in the different zones, and the proportion of- them at which Compound 
Ascidians were found, is necessary in order to give a more complete idea of the bathy- 
metrical distribution of the collection : — 
In 32 dredgings at from 0-50 fathoms, Ascidise Compositse occurred 16 times,^ or at 50 per cent, of the Stations. 
„ 51 
„ 50-500 
JJ 
)> 
14 „ 
27 „ 
55 
„ 23 
„ 500-1000 
55 
1 „ 
4 „ 
55 
„ 94 
„ 1000-2000 
55 
1 „ 
1 „ 
55 
The column of percentages brings out very clearly that the Compound Ascidians are 
raaiidy a shallow-water group, that they are abundant around coasts in a few fathoms of 
^ Including a few localities which were not Stations, such as Bermuda, Bahia, Simon’s Bay, Port Jackson, &c, 
