172 Annals of the South African Museum. 



(41). 40. Middle and hind tibiae without calcaria; no clavate hairs present. 



Cardiocondyla, Emery. 



(40). 41. Middle and hind tibiae with calcaria ; if not, then the erect hairs on 

 the body are more or less clavate. 



(47). 42. Posterior border of the clypens raised in the form of a trenchant 

 ridge bordering the antennal fossa (rather feeble in Rhoptromyrmex) . 



(44). 43. Epinotum unarmed ; no antennal scrobe. First joint of petiole 

 usually laterally compressed . . Rhoptromyrmex, Mayr. 



(43.) 44. Epinotum armed ; antennal scrobes usually present. 



(46). 45. Erect hairs simple .... Tetramorium, Mayr. 



(45). 46. Erect hairs usually trifid. Nodes of petiole usually strongly trans- 

 verse .... Sub-genus Triglyphothrix, Forel. 



(42). 47. Posterior border of the clypeus not raised in the form of a ridge. 



(49). 48. Flagellum without a distinct club; £ £ polymorphic. 



Hessor, Forel. 



(48). 49. Flagellum with a more or less distinct club. 



(51). 50. Clypeus usually bicarinate ; £ £ rarely polymorphic. 



v Monomorium, Mayr (part). 



(50). 51. Clypeus not bicarinate, occasionally with a median carina. 



(53.) 52. ^ $ strongly dimorphic, consisting of 1/. 11 with very large heads, 

 and an ordinary $ caste ; more rarely polymorphic (sub-genus 

 Allopheidole) .... Pheidole, Westwood. 



(52). 53. £ $ monomorphic. 



(55). 54. The peduncle of the 1st joint of the petiole very long ; thoracic 

 sutures almost or entirely obliterated . . Ocymyrmex, Emery. 



(54) . 55. The peduncle of the first joint of the petiole not very long. 



(57). 56. Epinotum unarmed ; erect hairs not clavate ; no antennal scrobes. 



Tetramyrma, Forel. 



(56). 57. Epinotum usually armed ; erect hairs clavate; a shallow indication 

 of the antennal scrobes sometimes present. Middle and hind tibiae 

 without calcaria ..... Leptothorax, Mayr. 



The above key applies only to the species so far known from South 

 Africa. In many species of Pheidole the club of the antennae is by no 

 means sharply defined, hardly more than in the genus Messor, but in 

 the latter genus the largest workers are connected with the smallest 

 by a gradual series of intermediate forms, and the head, although 

 perhaps much larger, does not differ materially in shape from that of 

 the smallest workers. In Pheidole, on the other hand, the workers 

 are dimorphic (with the exception of the sub- genus Allopheidole, in 

 which there are intermediate grades between the % and the $ ) } the %. 

 being sharply differentiated from the $ , and having a differently 

 shaped head. 



In some species of Leptothorax, the posterior margin of the clypeus 

 is slightly raised in a ridge posteriorly, but the clavate hairs and the 

 absence of calcaria to the middle and hind tibiae will serve to dis- 

 tinguish them from the members of the tribe Tetramoriini. 



