Of earth and air and water, growing more
And louder, shriller, heavier, a roar
Up the dun atmosphere did overwhelm
His ears; and as he looked affrighted round
Every manner of beast innumerable
All thro' the shadows crying grew, until
The wailing was like grass upon the ground.
Asudden then within his human side
Their anguish, since the goad he wielded first,
And, since he gave them not to drink, their thirst,
Darted compressed and vital.—As he died,
Low in the East now lighting gorgeously
He saw the last sea-serpent iris-mailed
Which, with a spear transfixèd, yet availed
To pluck the sun down into the dead sea.

 Compare the Beast that emerges from the sea in The Book of Revelation; see Rev. 11:7, 13:1-10, and 13:11-18. The Beast isn’t very serpentlike, but is given power by The Dragon (the serpent, or Satan).
And the Last Day Being Come Man Stood Alone