After having examined Gray’s type of Acanthomys leucopus) and compared that animal with my description of Mus leucopus ²), Alston comes to the conclusion 3), “that I have been misled by Gray’s very insufficient description”. I am the first to agree with Alston in this statement. I am much indebted to Mr. Alston for his minute description of the Mus in question, s. n. Mus terrae-reginae. If I had known that Gray’s leucopus has the tail shorter than head and body and the fur above dark reddishand not greyish-brown, I should certainly not have made a mistake in confounding these two distinct species. But I believe it quite impossible to recognize species if they are described so incompletely and inexactly as is the case with the greater part of Gray’s descriptions.