REPORT ON THE TETRACTINELLIDA. 
403 
Successful hauls were made from — 
3 out of 55 Stations 
on Globigerina ooze 
or 
5-46 
per ( 
3 
J5 
50 
red clay 
5) 
6 
55 
1 
JJ 
9 
gravel 
5) 
IM 
55 
7 
?5 
48 
blue mud 
>> 
14-58 
55 
5 
30 
volcanic mud 
16-6 
55 
4 
21 
JJ 
green sand and mud 
19 
55 
2 
10 
>> 
Pteropod ooze 
55 
20 
55 
4 
20 
M 
coral mud 
55 
20 
55 
3 
13 
>> 
hard ground 
55 
23 
55 
1 
4 
JJ 
Diatom ooze 
55 
25 
55 
3 
j) 
8 
)) 
sand 
55 
37-5 
55 
The poverty of the Glohigerina ooze is very remarkable, but no doubt it stands in 
relation to the fact that the Tetractinellida are comparatively rare in deep water, such as 
that in which the Globigerina ooze usually occurs ; but one would scarcely have expected 
the ooze to prove poorer than the red clay. Conversely the comparative richness of coral 
mud, sand, and hard ground is connected with the greater abundance of Tetractinellids in 
shallow water. The comparative richness of Diatom ooze on the other hand is probably 
due to the fact that the Tetractinellida and probably other S|)onges also find in the 
Diatoms an abundant source of food supply. 
The comparative richness of the Indo -Antarctic region is probably connected with the 
unusually numerous dredgings made off Kerguelen, and partly with the fact that it lies 
within the zone of the Antarctic Diatom ooze ; it is true that the bottom from whence the 
Tetractinellids were obtained is recorded as volcanic mud, and coarse gravel, but this 
is in shallow water; in the deeper water on each side of the area from which the Sponges 
were obtained the Diatom ooze occurs, and it would appear very probable that it is 
also present in the shallower deposits, but masked by the abundance of volcanic material ; 
this is just one of those cases on which the analysis of the deposit as made by Dr. Murray 
is likely to throw light ; but the view I have expressed is confirmed by the fact that 
Diatoms abound in the vestibules and cloacas of the specimens of Cinachyra harbata, 
a species rich in individuals which inhabit the volcanic mud off Kerguelen. 
It now only remains to add a short summary of the distributional characters of the 
subdivisions of the Tetractinellida. The Choristida are cosmopolitan, with a wide bathy- 
metrical range, extending from the coast-line to a depth of 2000 fathoms. Judged from 
the results of the Challenger Expedition, the zones from 0 to 50 and from 51 to 200 
fathoms are equally rich in species ; judged from the entire body of recorded observa- 
tions (tabulated on p. 378) the former is the richer in the ratio of 100 : 68. Since the 
littoral zone is more accessible to general observation this gives too high a value for the 
littoral zone, while that deduced from the Challenger is for obvious reasons too low. 
