The incident happened yesterday when a Border Security Force (BSF) patrol near the Kalanchi border out post in the North 24 Parganas district detected some suspicious movements.
When a group of about four people was challenged by the force personnel, the suspects threw away the bags they were carrying and later 21 'Star' tortoises were recovered from them, the officials said.
The rare tortoise variety (Geochelone Elegans) is notified as secure under the 'Wildlife Protection Act' and the global 'Convention on International Trade in Endangered Species' (CITES).
"The estimated value of the seized tortoises is about Rs 12.6 lakh," a senior BSF officer said.
In an another incident along the same border, BSF troops seized gold and silver worth about Rs 37.54 lakh today when the cache was being smuggled from across the Banpur border post in Nadia district of the state.