14 Merriam Mammals from Tres Marias Islands. 



species from the mainland, and find that they differ in such pro 

 nounced characters that I am forced to describe them as distinct. 

 One of the bats also is here described as new. 



The raccoon was recorded in ' Biologia ' as the South Ameri 

 can Procyon cancrivorus, but with a series of eight specimens before 

 me 1 am unable to detect any characters by which it can be re 

 ferred to that species. Its affinities, on the other hand, are dis 

 tinctly with P. lotor and P. lotor hernandezi, of which it appears 

 to be merely a pale form, possessing slight though constant 

 cranial differences. In view of these facts, I have described it 

 as a new subspecies of lotor. Those who insist on intergradation 

 as the touchstone of subspecies will have to set it up as a full 

 species. 



The alleged occurrence of P. cancrivorus on the Tres Marias is 

 cited in ' Biologia ' " as furnishing another instance of the pecu 

 liar affinity of their fauna to that of Southern Central America '' 

 (p. 209). Mr. Nelson's collections, however, show that not only 

 the raccoon and all the other mammals, but also the birds, rep 

 tiles, and plants, are closely related to species now living on the 

 adjacent mainland of Mexico. 



One of the bats obtained by Mr. Forrer is recorded by Mi. 

 Thomas as a young specimen of Cheer onycteris mexicanus. Inas 

 much as this species was not obtained by Mr. Nelson, whereas 

 the commonest bat of the island, a Glossophaga, was not recorded 

 from Forrer's collection, and since the two genera are closely re 

 lated, is it not possible that a reexamination of the Forrer speci 

 men will show it to be a Glossophaga instead of a Choeronycteris f 

 Assuming this to be the case, 10 indigenous land mammals are 

 known from the islands. Of these, five, or exactly half, are bats ; 

 of the others, one is a Marsupial ; one a Carnivore, and three are 

 Rodents. 



Of marine mammals three are recorded, a seal and two por 

 poises, but since only one of these was obtained, the identifica 

 tion of the other two is uncertain. 



Marmosa insularis sp. nov. Tres Marias Pigmy Opossum. 



Type from Maria Madre Island Mexico. No. 89215 J* ad., U. S. Nat. 

 Mus., Biological Survey Coll. Collected May 16, 1897, by E. W. Nelson 

 and E. A. Goldman. Original No. 11028. 



Characters. Size and general appearance as in M. canescens, but ears 

 larger, tail longer, fore feet smaller, color more fulvous, skull longer and 

 more slender. 



