Please get him to a vet as soon as possible.
From www.anapsid.org "It is important for the wound to be thoroughly cleaned and all loose pieces to be removed from the cracked shell. Injectable antibiotics should be given. Turtles can get a serious disease called peritonitis and septicemia..."
Here are some sites for other tips about what to do, please read them carefully.
http://www.turtlecare.net/repair.htm
http://www.austinsturtlepage.com/Care/m ... ed%20Shell:
what you should expect from the vet: http://www.anapsid.org/shellrepair.html



