From Dragon Mania Legends Wiki
The Clam is a feature added in Update 2.0 and it is located between the Main Island and the smaller island branching off of it. When subscribed to, it gives the Trainer an initial number of Gems and then an additional fixed number of Gems per day upon opening the Clam, both in accordance to the subscription. This subscription will last for 30 days. Any Gem collected from the Clam is added to the user's VIP level. The user has 24 hours to collect the Gems for that day, otherwise they are lost. The icon will be shown atop the Clam whenever it is ready to give the Gems for that day while the icon will be shown whenever there is an ongoing offer for the Clam.
|Subscription||Initial Gems||Gems per Day||Total Gems||$ Cost|
Prices for the same offer may vary by location and/or even by platform.