A MONOGRAPH OF THE BATS OF NORTH AMERICA. 75 



one of personal equation. To express it differently, tlie membranes 

 are lightly pigmented, though the pigment is black in color. The an- 

 terior surface of the interfemoral membrane appears to be less pig- 

 mented than other portions of the wing membranes. As a result the 

 membrane i)reseuts a whitish appearance, as though a little chalk 

 and water had been lightly painted over it. The post calcaral lobe is 

 often well developed, but on the whole is inconstant. 



The cliaracters of the eastern species are seen in the diagnosis and 

 des(!ription of V. gryphiis, and are in contrast to the western. 



The distribution of the genus Vespertilio in North America is similar 

 to that of other genera of mammals whose range is extensive. Thus it 

 can be said that the western forms in the United States (west of 98°) 

 are distinct from the eastern; that the eastern forms range north and 

 northwest through British America with little variation, and that they 

 are disposed to reai^pear in the mountain ranges of the northwestern 

 United States along the Pacific coast, presumably by migration Irom 

 the north along paths of high altitude; that the southern parts of the 

 eastern United States, say from below 30° latitude, resemble Mexican 

 phases, as do those of the western, from an irregular line between 36° 

 and 42° latitude. 



The species of the genus, therefore, are the least local of any mem- 

 bers of the fauna. It is probably true that all of its representatives 

 have been derived from one or more tropical ancestors, and that an 

 exhaustive knowledge of these forms will be required before the pecu- 

 liarities of the more northern phases can be properly interpreted. As- 

 suming that migrations have taken place from the south to the north, 

 the lines of their first divergence would appear to have occurred in the 

 northern parts of Mexico in three separate trends — one to the northeast 

 through the Gulf States; one due north through Arizona and New 

 Mexico, and one northwest through the Sacramento Valley. At points 

 farther north the lines become greatly disturbed, the tropical features 

 are to a great extent lost, and the study of individuals becomes one of 

 great intricacy. Greatly extended research beyond the means available 

 to the writer will be needed before the questions of distribution and 

 the validity of zoological varieties can be determined. The conclu 

 sions at present thought to be tenable may serve a useful purpose 

 until the question can be settled by students who are more favorably 

 situated than he. 



1. Vespertilio gryphus Fr. Cuvier. The little Brown Bat. (Plates x. xi.) 



VcHjurliUo fjryphus Fr. Cuvier, Nouv. Aniial. dii MustMuii, I'aiiH, 1832, 15. 



J'eajHrtilio salurii, ibid. 



VegpertiUo suhflainis, ibid. 



Vespertilio caroli Temminck Monoj;. Mam. Il, 1835, 237. Wa^fuer, Selnvb. Saiigeth., 



Snppl., V, 1855, 749; Dubsou, Cat. Chirop. Brit. Mus., 1878, 325. 

 Vespertilio domestical^ (ireeu, Cab. Nat. Hist., II, 290. 



