NEW FORMICID/E FROM BARRO COLORADO ISLAND. 15! 



from female specimens taken on the island of St. Thomas, W. I., 

 in a nest of Cardiocondyla emeryi Forel. 



(7) Bruchomyrma acutidens Santschi (1923), described from 

 female specimens taken by Carlos Bruch in Argentina in the nest 

 of Pheidole str obeli richteri Forel. 



Besides the accounts of these extreme, workerless, permanent 

 parasites numerous scattered and more or less incomplete notes 

 have been published on other types of social parasites within the 

 tropics. No slave-making ants have been recorded, but certain 

 African and Malagasy species of Crematogaster of the subgenera 

 Oxygyne and Atopogyne are probably temporary parasites in the 

 nests of species of the typical subgenus Crematogaster, and the 

 phenomenon known as "parabiosis," as Forel (1898), Mann 

 (1912), and I (1913, 1 92 1 a) have shown, is well-developed among 

 certain neotropical ants belonging to several genera (Dolichoderus, 

 Crematogaster, Odontomachus, Camponotiis] . There is, moreover, 

 in the tropics of both hemispheres a long series of tiny "thief," or 

 lestobiotic ants, which belong to the Myrmicine genera Solenopsis, 

 Oligomyrmex, Aeromyrma, Pcedalgus, Carebara, Erebomyrma, 

 Tranopelta, Liomyrmex, Pheidole, Xenomyrmex, Monomorium, 

 etc. and live in or very near the nests of other ants or of termites. 



During late July and early August, 1924, while studying the 

 exuberant ant-fauna about the new tropical laboratory on Barro 

 Colorado Island, in the Panama Canal Zone, I repeatedly came 

 upon a small and peculiar Megalomyrmex living in the fungus 

 gardens of a Sericomyrmex. Since the behavior of these insects 

 represents a new type of symbiosis or xenobiosis, I here describe 

 them, prefacing my account of each with a few historical notes. 

 The taxonomic descriptions of the two ants and of some small 

 lestobiotic species associated with the Sericomyrmex colonies are 

 placed at the end of the paper. 



Our knowledge of the habits of the Attine ants of the genus 

 Sericomyrmex is rather meager. The earliest and best account is 

 that of Urich published as early as 1895. It refers to a Trinidad 

 species, later described as 5. urichi Forel, but at the time of 

 Urich's writing supposed to be opacus Mayr. 'The nests of 

 these ants," he says, "are found commonly about Port of Spain, 

 in gardens, in the grass as a rule, but sometimes in the flower beds, 



