396 
THE YOYAGE OF H.M.S. CHALLENGEK. 
Table V. 
I. 
0-50 
Fathoms. 
II. 
51-200 
Fathoms. 
III. 
201-1000 
Fathoms. 
IV. 
Above 
1000 
Faths. 
Tetractinellida, . 
9 
8 
14 
8 
Actual number of successful hauls. 
5-06 
3-54 
4-17 
1 
Proportional number at different depths. 
Hexactinellida, . 
7 
22 
28 
Actual number of successful hauls. 
0-84 
1-8 
1 
Proportional number at different depths. 
Monaxonida, 
6 
16 
15 
15 
Actual number of successful hauls. 
1-786 
3-714 
2-375 
1 
Proportional number at different depths. 
Ceratosa, 
7 
3 
1 
Actual number of successful hauls. 
13-1 
4-374 
1 
Proportional number at different depths. 
Calcarea, 
5 
6 
2 
Actual number of successful hauls. 
4-327 
4007 
1 
Proportional number at different depths. 
The foregoing results can be most plainly expressed by curves, such as are given in 
the table on p. 397. These have the further advantage of representing not only the bathy- 
metrical distribution of each group, but its richness as compared with the other groups. 
The curves are obtained by measuring off on the ordinate IV. a number of units 
equivalent to the number of species or successful stations met with within that range of 
depth, and then measuring off on the other ordinates lengths equal to the first multiplied 
by the proper numbers given in Table lY. Thus in the case of the curve of the 
Tetractinellida the number of species obtained between 1000 fathoms and greater depths 
is eight, this multiplied by the numbers 9, 11, and 5 ’4 gives the lengths to be measured 
off on the ordinates I., II. , and III. 
An inspection of this table shows that, relatively to the total number of hauls made, 
about as many species of Sponges were obtained between the depths of 51 and 200 
fathoms as between 0 and 50 fathoms, but beyond the depth of 200 fathoms the number 
fell very rapidly, and still more rapidly beyond the depth of 1000 fathoms. As regards 
stations it will be observed that the maximum of successful stations lies on the ordinate 
II., the curve falling rapidly towards the ordinate L, and also, but not quite as rapidly, 
towards ordinate III., past this, however, there is a very sudden drop, the curve 
descending almost parallel with that of species, which is due to the fact that in deep- 
water stations seldom more than one species was obtained at each. 
A great difference is to be observed in the behaviour of the station curve and the 
species curve in the case of the Monaxonida : the species curve culminates on the first 
ordinate, and then descends almost in a straight line to ordinate III., past which there 
is a rapid descent ; the station curve on the other hand culminates on the ordinate II. of 
