species includes the general area of these countries: India(英语:List of non-marine molluscs of India), Sri Lanka(英语:List of non-marine molluscs of Sri Lanka)
Census Bureau. 2021-04-26 [2021-04-26]. (原始内容存档 (PDF)于2021-04-26). State Area Measurements and Internal Point Coordinates. Washington, D.C.: U.S. Census
各國高等教育程度(英语:List of countries by tertiary education attainment) 各國中等教育程度(英语:List of countries by secondary education attainment) 世界大學網路排名 英孚英语水平指数 国际学生能力评估计划 促進國際閱讀素養研究
Wealth. The New Press. 2006. US Census Bureau report on educational attainment in the United States, 2003 (PDF). [2006-07-31]. (原始内容存档 (PDF)于2021-10-02)