With a name like Arche Noah, it should come as no surprise that you want to collect animals in pairs.
At the start of the game, players receive one animal card face down from the shuffled deck; the deck includes ten types of animals, with cards numbered 1-4 for each type. The player looks at this card in secret, and takes 10-12 purple chips and 2-3 green chips, depending on the number of players.
Each round, animal cards are revealed equal to the number of players. In clockwise order from the starting player, each player bids a number of purple chips, then starting with the high bidder (going clockwise from the starting player in case of ties), each player takes one animal card and places it face down on his stack. If a player discards one of his green chips, he takes two animals instead, stiffing whoever comes last in the round!
After all of the animals have been claimed, players reveal their collection. Pairs of the same type of animal score the sum of their numbers; if you have all four animals (two pairs), you receive 3 bonus points; if you have an animal which is not part of a pair, you lose points equal to its number. Each pair of purple chips is worth 1 point.
After tallying the points, players shuffle the cards, refill their purple chips, receive one animal in secret, then play another round. At the end of that round, players score again, this time receiving 1 point for each green chip still in hand. Whoever has the highest total over two rounds wins!