The cover was fastened with a wooden button.
The substitute assistant, after a deal of futile and exasperating poking with the handle of the net, managed to turn the button and throw back the leather-hinged cover.

Through the square opening the water beneath looked darkly green.

There was much seaweed in the car, and occasionally this weed was stirred by living things which moved sluggishly.
John Brown reversed the net, and, lying flat on the wharf, gingerly thrust the business end of the contrivance through the opening and into the dark, weed-streaked water.

Then he began feeling for his prey.
He could feel it.

Apparently the car was alive with lobsters.