l6O WILLIAM MORTON WHEELER. 



were not available, they manured the garden with numerous 

 golden yellow droplets of their own feces. In two of my nests 

 the gardens were suddenly blasted in a peculiar and unexpected 

 manner. Bits of mango had been left in the Petri dishes and had 

 decomposed during the night. This decomposition seemed to be 

 due to some bacterium which was accidentally transferred to the 

 gardens, probably on the feet and mouthparts of the ants, and at 

 once overwhelmed the fungus, so that within a few hours it 

 shrivelled up and turned black. The ants, apparently quite 

 unable to prevent the inroads of the lethal microorganism or to 

 restore their fungus to its normal condition, became demoralized 

 and eventually wandered away from it to other parts of the dishes. 



The population of the Sericomyrmex colonies which I examined, 

 resembled that of Trachymyrmex colonies, the smaller nests con- 

 taining between 100 and 200, the largest (a single nest) about 300 

 ants. No incipient colonies were seen, but there can be no doubt 

 that the recently fecundated queens establish their colonies and 

 gardens in the manner described by von Ihering, Huber, Goeldi 

 and Bruch for various South American species of Atta and 

 Acromyrmex. 



The guest-ant, which I found in ten out of the twelve Seri- 

 comyrmex nests excavated in the immediate vicinity of the 

 laboratory on Barro Colorado Island, is obviously a species of 

 Megalomyrmex, a peculiar neotropical genus established by Forel 

 in 1884 for a Colombian ant, M. leoninns and now known to 

 comprise some 15 species which range from Bolivia to Mexico. 

 While the generic name was appropriate to the type and several 

 other species, which measure nearly a centimeter in length, it is a 

 misnomer for several much smaller species gceldii Forel, pusillus 

 Forel, ivallacei Mann, silvestrii Wheeler and sjostedti Wheeler 

 which have been recently described. The known species of the 

 genus are divisible into two groups, one of which, including the 

 type, has convex, coarsely 5- or 6-toothed mandibles, with a sharp 

 angle between their apical and basal borders, whereas in the other 

 group, comprising only two species, silvestrii and sjostedti, the 

 mandibles are narrower and more flattened, with a rounded angle 

 between the basal and apical borders and the latter with two large 

 terminal teeth and a series of very minute basal denticles. This 



