Notes on Commensal Rats

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  • United States National Museum, Division of Mammals, Washington, D. C.

In the course of a study on the origin, distribution and ecology of commensal rats a few facts have become apparent which, I believe, are important enough to be published even before the general account is completed.

1. COMMENSAL RATS OF NORTH AMERICA All the American literature dealing with rats, systematic, ecological, medical, considers three types of these animals: viz. the Norway rat (Rattus norvegicus Berkenhout), the Black rat (Rattus rattus rattus Linnaeus), and the Roof rat (Rattus rattus alexandrinus Geoffroy). This classification, apparently taken from Miller (1924), does not quite cover the facts. The true R. r. alexandrinus Geoffroy is not the animal usually referred to under this name. It has a brown back and grey belly, the two colors gradually passing into one another without any line of demarcation. The other animal, usually referred to as alexandrinus, has a brown back also, but the underside white or lemon yellow and sharply set off from the back.