A Monograph of the Formicidae of South Africa. 173 



The frontal carinae in Melissotarsns are placed close together as in 

 the genus Sima, but the absence of thoracic sutures, the structure of 

 the metatarsus, and the 6-jointed antennae easily serve to distinguish 

 them from the latter s;enus. 



Section I. PROMYRMICINAE, Emery. 

 Tribe PSEUDOMYRMIM, Forel. 



Genus SIMA, Roger. 

 Berlin. Ent. Zeitschr., vol. 7, p. 178, 1864. 



Characters. 



£ . Head more or less rectangular, somewhat truncate in profile 

 anteriorly, the clypeus and mandibles being placed vertically below 

 the anterior face of the head ; antennae 12 -jointed, slightly thickened 

 towards the apex ; eyes usually very large. Thoracic sutures distinct ; 

 the metanotum, usually not recognisable in the majority of £ ants, 

 is more or less distinct in this genus. Epinotum high, unarmed. 

 Abdomen more or less cylindrical and elongate. Sting exserted. 

 £ ^ dimorphic in 8. ambigua, race rhodesiana, but the dimorphism is 

 confined to the structure of the head. 



$ & ^ . Very similar to the $ , except for the usual sexual differ- 

 ences in the structure of the thorax. <$ , antennae 13-jointed. 



The members of this genus are almost all tree-ants, nesting in 

 hollow twigs or thorns, or in hollow reeds. Our two commonest 

 species, ambigua-rhodesiana and natalensis-bulawayana, are very partial 

 to the Acacia horrida. They are very quick ants, and have a habit of 

 sliding, on the approach of danger, to the opposite side of the leaf 

 or branch, or of dropping to the ground. The sting is powerful, and 



readily used. 



v 

 Key to the Species of Sima, <£> 9 •* 



(2). 1. Large and stout species. Frontal carinae wider apart than in the other 



species of the genus ; 3 ocelli well developed. 



(Sub-genus Pachysima, Emery), aethiops, Smith. 

 ( 1 ) . 2. Smaller and more slender species ; frontal carinae closer together. 

 (6). 3. Pronotum with distinct anterior angles, sharply margined. 2 or 3 



distinct ocelli .... (sub-genus Sima, s. str.) 



(5). 4. Colour yellow or brownish yellow ; 6-8 mm. long natalensis, Smith. 



* I am indebted to Prof. Emery for valuable advice in the construction of 

 this key. 



