def extract_valid_capabilities(capabilities):
    """
    Extract valid capabilities from a list.

    Args:
        capabilities (list): List of tuples containing capability information.

    Returns:
        list: List of valid capabilities.
    """
    return [cap for cap in capabilities if len(cap) == 4]

# Example usage
capabilities = [('evolved_verified_generate_test_1768680667', 4235.89001196408, 51, 8305.7),
                ('verified_default', 4235.0, 51, 8303.9),
                ('evolved_verified_create_memory_1768424362', 4235.89001196408, 52, 8145.9)]

print(extract_valid_capabilities(capabilities))