Can turtle shells be declared and imported into China?

I can't. According to official website of China Customs, China joined the Washington Convention in the last century, and all internationally endangered animals and plants and their products listed in the international treaties on customs protection in China are prohibited from entering or leaving the country. Including tortoise shells. Tortoise shell is also called tortoise shell, which is the name of traditional Chinese medicine. It's a tortoise's carapace and bellybutton. It has the effects of nourishing yin, suppressing yang, invigorating kidney, strengthening bones, nourishing blood and heart, consolidating menstruation and stopping metrorrhagia.