146 WILLIAM MORTON \VHEELEK. 



is not a monotypic genus but comprises also several South 

 American species. At least Professor Emery writes me that he 

 has in his collection two species which seem to belong to the new 

 genus. Both of these are represented by female specimens only. 

 One is from Bolivia, the other from Rio de Janeiro. 



Comparatively little is known concerning the ethology of the 

 Solenopsidii apart from the genus Solenopsis, which has many 

 representatives in Europe and North America. The majority of 

 the species belonging to the tribe, if we except Pliddologeton and 

 the larger forms of Solenopsis, like 5. gcininata, appear to have 

 certain common ethological traits of more than usual interest. 

 These characters, which were first appreciated by Forel, and con- 

 stitute one of the many fine discoveries of that able naturalist, 

 are the following : 



i. The males and especially the females of the smaller species 

 of Solenopsis, the species of Aeroinyrma, Carebara, Oligomyrmcx, 

 and presumably also of Tranopclta, are of very large size com- 

 pared with the workers. The same is also true of PJieidologe- 

 ton and the polymorphic species of Solenopsis when the sexual 

 forms are compared with the most diminutive caste of workers. 

 The relative dimensions of the queens differ, however, consider- 

 ably in the different genera. Thus in our common North Amer- 

 ican Solenopsis nwlesta the workers measure 1.5 mm. in length, 

 the females 4.5-5 mm.; while in Carebara lidna the worker is 

 hardly larger than that of S. nwlesta (1.52 mm.) whereas the 

 female is of gigantic dimensions (23 mm.). The dimensions of 

 Erebomyrma Longii lie between these extremes, though much 

 nearer to those of >$. inolcsia. The worker is 1.5-2.25 mm. long, 

 the female 8-8.5 mm. If we cube the dimensions in these three 

 species and make due allowance for the fact that the body of the 

 female ant is in each case proportionally much thicker than that 

 of the worker, we have the following roughly approximate ratios 

 between the volumes of the workers and females : 



Solenopsis molest a, \ : 20. 



Erebomyrma Longii, 1:150 



Carebara vidua, I : 2000. 



These are rather extraordinary dimensions for queens as com- 



