212 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 69 



collected by J. H. Batty on Coiba Island. In reduced size, most 

 obvious in the length of the skull and toothrows, this example agrees 

 closely with the Mexican form which is probably a small, geographic 

 race of Natalus stramineus. 1 The forearm measures 38.4 and the 

 upper toothrow (front of canine to back of posterior molar) 64 

 millimeters. 



Specimens examined: Coiba Island, I.' 



Family VESPERTILIONIDAE. Common Bats 



Most of the common bats of northern latitudes are included in the 

 family Vespertilionidse which, with several subfamily divisions, 

 ranges over the greater part of the land surface in both the eastern 

 and western hemispheres. The Isthmian members of the family are 

 distinguishable externally by the combination of medium or small 

 size, slender general structure, simple noses, narrow, usually pointed 

 ears, slender tragus, long tail reaching to near posterior border of 

 wide interfemoral membrane, and absence of adhesive disks on the 

 soles and thumbs. A notable feature of the skull is a broad and 

 deep U-shaped median, anterior emargination of the palate and the 

 resultant obliteration of palatal branches of the premaxillae. Five 

 genera are now known to represent the family in Panama. 



Genus MYOTIS Kaup 

 The bats of the genus Myotis superficially resemble those of 

 several related genera and examination of skulls is often desirable 

 in order to make positive determinations. The two known Panama 

 representatives are, however, usually recognizable by the combina- 

 tion of color and size ; the colors are dark brown or blackish and the 

 length of the forearm 34 to 36.5 millimeters. They thus exceed the 

 measurements of Rhoge'essa and do not attain the dimensions of the 

 other Vespertilionine genera of the region. The skull of Myotis is 

 slender and of rather delicate structure, the braincase rounded and 

 usually rising high behind the narrow, depressed rostrum. Three 

 upper premolars are normally present on each side, and the teeth are 

 normally 38 in number. In certain species a pair of small obsolescent 

 upper premolars may be present or absent. 



1 In describing Natalus mexicanus Mr. Miller used for comparison specimens 

 from Dominica as representing N. stramineus, whose exact type locality, how- 

 ever, remains undetermined. 



2 Collection Amer. Mus. Nat. Hist. 



