404 
THE VOYAGE OF H.M.S. CHALLENGER. 
Beyond 200 fathoms the number of species rapidly falls ojff, as shown both by the 
Challenger results and those of other expeditions ; from the sum total of observations 
we obtain the following proportion : — Number of species obtained from 0 to 50 : that 
from 201 to 1000 : that from 1001 and over = 100 : 35 : 7'4. 
Certain families enjoy a wide bathymetrical range, as for instance the Tetillidse, 
which extend from 0 to 1000 fathoms, as many species being recorded from 0 to 50 as 
from 50 to 1000 fathoms. 
Others are more restricted, either affecting deeper water, as the Theneidse, or 
shallower, as the Stellettidae. The former family, with the exception of a single genus, 
doubtfully assigned to it [Placortis), is confined to continental or abyssal depths, an equal 
number ranging from 51 to 200 fathoms and from 201 to 1000. The genus Thenea 
is the characteristically deep-water genus of the Tetractinellida, the shallowest water 
from which it has yet been recorded being 78 fathoms, the deepest 1913 fathoms. The 
Stellettidae are usually found in water under 50 fathoms deep, the greatest depth 
attained (250 to 400 fathoms) is that recorded by Weltner for the curiously specialised 
Trihrachium schmidtii, which would thus seem to possess a wide range, since it was 
obtained by the Challenger in from 7 to 20 fathoms off Bahia. 
The Geodidse, with a wider range than the Stellettidse, are also commoner in deeper 
water (compare table on p. 378). 
The Lithistida are more limited in range than the Choristida, seldom occurring 
either in such shallow or such deep water as the latter, the minimum recorded depth 
is 7-|- fathoms [Corallistes typus, Jide 0. Schmidt), the maximum 1075 fathoms 
{Azorica pfeifferse, Challenger), the greatest number of occurrences are recorded from 
continental depths. Since the bathymetrical distribution of the Lithistida is regarded 
as of some importance by the palaeontologist I add a more exact discussion of this 
subject. In the following table are given the various depths from which Lithistids have 
been obtained, with the number of times from each : — 
0-50 
Fathoms. 
51-100 
Fathoms. 
101-150 
Fathoms. 
151-250 
Fathoms. 
251-3.50 
Fathoms. 
351-450 
Fathoms. 
451-1075 
Fathoms. 
1 at 7A 
1 „ 17 
1 „ 18 
1 „ 33 
2 „ 45 
1 at 56 
9 „ 65 
1 „ 86 
2 „ 100 
1 at 101 
1 „ 103 
2 „ 114 
1 „ 124 
1 „ 125 
1 „ 127 
1 „ 128 
1 „ 129 
1 „ 131 
1 „ 135 
7 „ 140 
1 at 168 
1 „ 180 
1 » 211 
1 » 212 
1 „ 220 
1 „ 240 
1 at 270 
3 „ 292 
2 „ 315 
1 „ 350 
4 at 374 
1 „ 435 
1 at 805 
1 „ 1075 
6 „ 27 
13 „ 71 
18 „ 126 
6 „ 205 
7 „ 303 
5 „ 386 
2 „ 940 
