epths sprang up the
sea-green stems of the fucus, twining round columns which sank far down,
and afforded them support. Here feathery tufts of green vegetables
floated upwards in the clear water, while others of various strange
shapes and hues formed recesses and arches, twisted and knotted in a
variety of ways. Fish, of varied forms and brilliant colours, darted in
and out among the openings, some rising close up to the boat, as if
curious to ascertain the character of the visitors to their submarine
palace.

"I wish the doctor were here to tell us their names," exclaimed Tom.
"Look there, at those odd creatures. What can they be?" The fish at
which he pointed were flat, of an oval form, and of a rich silvery
colour, delicately striped downwards with azure bands. They swam in a
perpendicular position, aided by two long and slender fins, one curving
upwards from the back, of a considerable length, and the other curving
downwards from the opposite side. There were many others differing in
form, but all of the most beautiful colours, darting and gliding in and
out, but, being apparently of a less curious or more timid disposition
than those which had excited Tom's astonishment, did not venture near
the boat. There were cray-fish, too, of large size, and enormous crabs,
and star-fish, and sea-urchins, and bivalves of various sorts clinging
to the rocks, with open mouths, to catch any unwary creatures coming
within their reach.

After enjoying the scene for some time, by giving a few strokes with
their oars the midshipmen allowed the boat to proceed further up the
cavern. Most of the party were hanging over the water with their noses
just above the surface, some with their hands trying to catch any of the
fish which might venture near, when a cry from Tim made them spring up.

"Shure, he'll be afther catching some of us, if we don't look out,"
exclaimed the Irishman, and at that moment they saw rising out of the
far depths of the cavern an enormous shark, his eyes glaring like two
glowing coals, as with open jaws he came nearer and nearer the boat.

"He'll be after swallowing the whole of us," cried Tim. "Back water!
back water!" To the Irishman the shark probably appeared much larger
than it really was.

"He won't do us any harm; but just keep the oars out of the water," said
Tom, who was, of course, obeyed, and the shark glided alongside the
boat, which he kept eyeing with suspicious glances.

"Would you