312 SNAKE FAUNA OF SOUTH AFRICA. 



The precise generic relationship of the genera of the Colu- 

 brinae is a difficult problem, for the known important characters 

 are few or uncertain, whilst the different genera mainly represent 

 the numerous comparatively slight variations in the arrangement 

 of the teeth — a character which alone is probably untrustworthy 

 in gauging generic affinities. An important character emphasised 

 by Boulenger is the presence of hypapophyses to the posterior 

 dorsal vertebrae, and several authors have pointed out that the 

 presence of these processes in all the Madagascar colubrines at 

 once separates them from certain American genera to which they 

 had been previously assigned. Nevertheless some American 

 genera do possess these processes, and indeed this character is 

 found in numerous genera distributed in all parts of the world. 

 In South Africa posterior hypapophyses are found in six genera, 

 but in all these genera, with one exception [Tropidonotus), the 

 pupil is vertically elliptic, whereas in all the Madagascar genera 

 the pupil is round. 



On the other hand, curiously enough, a round pupil is present 

 in all the South African genera, which are devoid of posterior 

 hypapophyses [Pseudaspis, Chlorophis , Philothamnus, Homalo- 

 satna), with the exception of Prosymna. It appears, therefore, 

 that in South Africa the two features of the Mada-eascar colu- 

 brines, presence of posterior hypapophyses and a round pupil, 

 are only to be found combined in one solitary snake, and that, 

 Ttopldonotus laevissimus, a South African representative of a very 

 widely distributed genus. This is peculiar in view of the fact that 

 these two characters occur together in Colubrines belonging to 

 many parts of the world. 



In East Africa a very similar state of affairs obtains, and, 

 judging from the list of species given by Tornier in his Reptiles 

 and Amphibia of German East Africa, 1895, most of the Colu- 

 brines of that region are without posterior hypapophyses and 

 the pupil is vertical ; and Tropidonotus olivaceiis is the only species 

 which has at the same time posterior hypapophyses and a round 

 pupil. 



It appears, therefore, that all the genera of Madagascar 

 Colubrines have preserved what must be regarded as the more 

 primitive characters the presence of posterior hypaponvhyses and a 

 round pupil, whilst in Southern Africa none of its peculiar genera 

 have retained both of these characters at the simc time ; but this 

 fact has no positive bearing on the question of the generic rela- 

 tionship of these snakes for a priori it is quite conceivable that the 

 South African colubrines arc immediately descended from forms 

 which were much like the Madagascar colubrines of the present 

 day. 



DIPSADOMORPHINAE. 



Madagascar has six genera of terrestrial OpistKbglyphous 

 Colubridae, of which five are peculiar to the region, and one genus, 

 Geodipsas, with two species in Madagascar, has also a solitary 

 representative in German East Africa. South Africa has the fol- 

 lowing genera belonging to this group : Pythonodipsas, Tarhophis , 



