of Edinhurgh, Session 1883-84. 
729 
in inverse ratio to the depth, although, of course, it by no means ex- 
cludes the possibility of other factors influencing their distribution. 
It is clear, then, that the only way of obtaining any satisfactory 
evidence on this point will be to take groups of different deposits 
of the same depth, and compare them with respect to their richness 
in Ophiurans, In many cases the range in depth of the deposits is not 
sufficient to allow of this ; but in some few instances it is possible. 
For example, dredgings were made on red clay at depths varying 
from 2250 to 3875 fathoms, and on Globigerina oo^e at from 1090 
to 2650 fathoms ; so that we may fake for comparison those 
instances of each which lie between 2250 and 2650 fathoms. 
Within these limits of depth the result is found to be — 
Globigerina ooze. Red clay, 
Ophiuroids present at . .1 . , ,5 stations. 
Number of dredgings, , ,9 , , ,19 
Whence it would seem that Ophiurans are nearly three times as 
widely spread on the red clay as on the Globigerina ooze. 
These figures are so strikingly at variance with those obtained 
from a consideration of the whole voyage that it is quite clear that 
there must be some flaw in the argument, which is probably to be 
found in the fact that the Globigerina ooze stations under considera- 
tion are the deepest examples of that deposit, while the red clay 
stations are the shallowest ; and from the general law of distribution 
according to depth, above alluded to, we should expect some such 
result as this to take place. 
None of the other deposits offer any adequate number of stations 
at equal depths for comparison ; so that it would seem that at present 
we have no sufficient data on which to base any safe conclusions 
as to the influence of the nature of the bottom on the presence or 
absence of these animals, although it is highly probable that such 
an influence is exerted. 
Possibly future investigations may make us acquainted with two 
areas which, being comparable in other respects, differ in the nature 
of the deposits forming their bottoms. 
In conclusion, I must express my indebtedness to Dr P. H. Car- 
penter for a quantity of valuable information from his journal relative 
to the dredgings of H.M.S. “Porcupine,” and to Mr Theodore Lyman 
for his courtesy in answering some questions which I addressed to him. 
