Matsya Purana 58.20

58.20

tāmrau kulīramaṇḍūkāvāyasaḥ śiṃśumārakaḥ.
evamāsādya tatsarvamādāveva viśāmpate!.. 58.19 ..

The turtle and the crocodile should be made of gold, the fish and the unvenomous water-snake should be of silver, the frog and the crab of copper, and the Siśumâra (porpoise) fish of iron. All these things should be prepared from before, O Lord of men.—18.