156 WILLIAM MORTON WHEELER. 



shall call amabilis. It is very closely related to 5. impexus 

 Wheeler of British Guiana, but the worker is somewhat larger, the 

 external borders of the mandibles are less convex, the meso- 

 thoracic tubercles are more acute and the silky hairs and pu- 

 bescence, especially on the upper surface of the body, are longer 

 and more conspicuous. The worker averages a little over 3 mm. 

 in length, the female somewhat more than 5 mm., the male about 

 3 mm. All the phases are ferruginous brown, the female being 

 decidedly darker and less reddish than the worker. Like most of 

 the smaller Attini, the workers are very timid and inoffensive. 

 When rudely touched they at once curl up and feign death. 

 Owing to their gentle disposition and graceful and deliberate 

 movements they are among the most fascinating ants to observe 

 in artificial nests. 



.S. amabilis is probably common in many parts of the jungle on 

 Barro Colorado Island but I was able to detect its nests only in 

 the recently made clearing and trails, where the red clay, which 

 gives its name to the island, is exposed to the sunlight, and there 

 only some hours after one of the almost daily, heavy showers. 

 As soon as the rain ceased the silky, mouse-like workers began to 

 bring up small pellets of earth and carefully deposit them in the 

 form of a loose crater around the entrance, which was about 3 

 mm. in diameter. These craters, which are completely obliter- 

 ated by each rain, are probably large and noticeable during the 

 dry season. As soon as one approaches the nest, the excavating 

 workers, like those of Trachymyrmex, either feign death and 

 become indistinguishable from the soil or hastily withdraw within 

 the nest entrance, so that the observer must remain motionless 

 for several minutes before they resume their labors. 



Most of the nests observed had a single crater and entrance, 

 with a slender gallery descending more or less obliquely to a 

 chamber about 4 to 6 inches beneath the surface, but a few large 

 nests resembled A tta nests, on a very diminutive scale in having 

 several entrances and craters and as many as 3 to 5 chambers, 

 scattered over an area of about a quarter of a square yard. The 

 chambers varied in size from that of a pigeon's to that of a hen's 

 egg, and were each filled with a fungus garden which was either 

 entirely built up on the floor and walls or partly suspended from 



