ON THE RELATIONSHIPS OF TAYLOR'S MOUSE, SITOMYS 



TAYLORI. 



BY 

 Frederick W. True, 



Curator of tlie Department of Mammals. 



In 1887, Mr. Oldfield Thomas described a very small mouse from San 

 Diego, Texas, under the name of IIe,^peromys ( Vesperiiinis) taylori* 

 Later ho gave a full description of it under the name of Cricetus {Ves- 

 per im us) taylori A 



For many years the National Museum possessed no examples of this 

 interesting little species except a mutilated skin inalcoh(>l, but on two 

 occasions since 1887 it has received some complete specimens in alcohol 

 from Mr. William Taylor, in whose honor the species was named. 



This mouse is readily distinguishable from other American iield-mice, 

 as Mr. Thomas has pointed out, by its small size and nearly uniform 

 coloration. 



Mr. Thomas placed it unhesitatingly in the subgenus Vesperlmus, and 

 remarked ''no detailed comparison is needed of this little mouse with 

 its nearest allies." I propose to show, however, that iti^ossesses char- 

 acters intermediate between those of Vesperimus and OnycJtomys, and 

 is typical of neither. 



Dr. C H. Merriam, in 1889, raised the subgenus Onyehomys of Baird 

 to the rank of a genus, giving as the principal characters the follow- 

 ing:! 



1. Anterior upper molar with three external and two internal cusps. 

 Last lower molar subcircular in outline. 



2. "Coronoid process of mandilde well developed, rising high above 

 the condylar ramus and directed backward in the form of a large hook." 



3. Nasals wedge-shaped behind. 



4. Body stout and heavy; tail short and thick. 



5. Hind feet with four phalangeal tubercles only. 



These characters are contrasted with those of Hesperomys § (especially 

 subgenus Vesperimus), in which the first upper molar has three cusps 

 on each side, the last lower molar is somewhat elongated, the coronoid 

 process is very short, the nasals are truncated behind, the tail is long, 

 and the hind feet have six tubercles. 



*Anu. & Mag. Nat. Hist., 5tli ser., xix, 1887, p. 66. 

 tProc. Zool. Soc, London, 1888, p. 446. 

 t North Amer. Fauna, 2, 1889, p. 3. 

 ^ = Sifomi/ii. 



Proceediugs National Museum, Vol. XVI— No. 972. 



757 



