A chelone in which head cannot be withdrawn completely inside the shell is

Options

A. Testudo
B. Chelonia
C. Trionyx
D. Both B and C

Answer

To solve the question "A chelone in which head cannot be withdrawn completely inside the shell is," we will analyze the options provided and identify the correct answer based on the characteristics of different types of chelonians (turtles and tortoises).

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for a type of chelonian (turtle or tortoise) where the head cannot be fully retracted into the shell.

2. **Review the Options**:
- Option 1: Testuda
- Option 2: Ceylonia
- Option 3: Trionix
- Option 4: Both B and C

3. **Analyze Each Option**:
- **Testuda**: This refers to tortoises. Generally, tortoises have the ability to withdraw their heads completely into their shells. Therefore, this option is incorrect.

- **Ceylonia**: This refers to a type of marine turtle, specifically the green turtle. Green turtles are known for their inability to retract their heads completely into their shells. This option is likely correct.

- **Trionix**: This refers to soft-shelled turtles. Soft-shelled turtles can retract their heads into their shells, although they do have a different morphology compared to hard-shelled turtles. Therefore, this option is also incorrect.

- **Both B and C**: Since we have established that Ceylonia is correct and Trionix is incorrect, this option cannot be correct.

4. **Conclusion**: Based on the analysis, the correct answer is **Ceylonia**, as it is a type of marine turtle that cannot withdraw its head completely into the shell.

### Final Answer:
The chelone in which the head cannot be withdrawn completely inside the shell is **Ceylonia**.

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