"Small pets are allowed if enclosed in a properly ventilated carrying case that can be held on your lap or stored under a seat." https://www.metrolinktrains.com/rider-info/onboard-policies/code-of-conduct/
You can also take them on the train in a IKEA bag if you cut holes out for the animals legs. All it needs to be is a carrying case/bag for the animal. Works everytime.
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