Possible Clues:

• Pets named Mary Shelly and Shell Silverstein, perhaps
• Galapagos slowpokes
• Shelled slowpokes
• Long-lived reptiles
• Slow animals
• Slowpokes in the animal world
• Books about advances restricting to reptiles
• Galapagos heavyweights
• Stories to confuse slow types
• Horny-shelled reptiles