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25 
part of this zone; they are much larger. It has been suggested 
that the increased size is an adaptation to catch the faint rays 
of light that penetrate to that depth. 
- The next zone. The turbot ( Pleuronectes maximus) and the 
skate (Raia latus), the representatives of this zone, are ground 
feeders, rarely coming to within 200ft. of the surface. The rays 
have a great geographical and vertical range. The Terebratulina 
caput serpentis has been found in the Hebrides of Scotland at a 
depth of 600ft. It has an enormous geographical and vertical 
range in the existing seas. The Challenger Expedition found it 
-at a depth of 6,500ft. off the Japan Islands. The ranges 
correspond closely with that of the Rays. We shall find, when 
we come to describe the fossils of the chalk, that it has an 
equally wide distribution as a fossil. 
The next zone, 600ft. to 1,700ft., is represented by Beryx 
splendens. This species has some affinity to the Beryx found as 
a fossil in the chalk. It frequents the seas off Madeira at about 
600ft., and was found off the Japanese Islands by the Challenger 
Expedition at 6,500ft. This fish is a good illustration of the 
increase of the size of the eyes at 600ft.,—the limit of light. I 
here quote from Professor Edward Forbes and Mr. Godwin 
Austin. Writing about the Madeira Fish Market, they say :— 
“The spring is characterised by the common appearance of the 
splendid coloured Beryx in the streets, attracting notice no less 
by its hues of silver, scarlet, rose, and purple than by the 
extraordinary and opalescent or rather brassy lustre of its 
enormous eyes.” 
The Hake (Merluccius vulgaris) is also a fish of very wide 
distribution, abundant in the deep waters of the British seas. It 
has been found at a depth of 2,500 feet. The family is very 
widely distributed. The Marine Zones are well defined and 
separated from each other; the limit of vegetation is inhabited 
by its own species of vegetable-eating mollusca and the fish that 
feed upon them, thus limiting the fauna to a small vertical 
range. The geographical range is also limited by cold, as we 
found in the example of the limpet. The greater geographical 
and vertical range of the fish inhabiting the deeper waters of the 
sea is a result of the uniformity of the conditions of their habitat. 
The vast area of the Deep Sea has no violent changes of tempera- 
ture to act as a barrier to their distribution, and the abundance 
of their food and power of locomotion enables them to inhabit 
this great ocean area—both geographical and vertical. I extract 
from the Challenger Reports the depth at which fish and 
mollusca have been found. The Deep Sea or abyssal fauna 
attains its most prolific development at a depth of from 8,600 
feet to 7,200 feet. There is a great abundance of Hewactinilid 
sponges, stalked crinoids, and sea urchins allied to Salenia. 
