Oti Some South African Aviculariidae (Arachnida). 133 



the whole form one series with the sigilla as a specific character 

 only ; but the difficulty of placing a form such as Gorgyrella in the 

 same genus as one such as Segregara seems greater than that of 

 separtiug such forms as constitute the so-called intermediate forms. 

 Both Simon and Purcell considered the character, when strongly shown 

 as above, to be more than specific, and so far as I am able to see, that 

 view is correct. 



The Ctenizidae are not alone in having muscle-scars or sigilla as a 

 generic character ; in the Eresidx, for example, the two genera Eresus 

 and Dresserus, of which the $ ? greatly resemble each other, can be 

 separated at a glance owing to the dorsal abdominal sigilla. The two 

 anterior pairs of muscle attachments are close together in Dresserus 

 and separate in Eresus ; in addition Dresserus is distinct in having 4 

 small cribellal plates instead of 2 large ones. The point, however, is 

 that the character, though scarcely so important as the differences 

 which exist in the Ctenizidae, is nevertheless of generic significance ; 

 so that it seems justifiable to consider that, although the genera of 4- 

 luuged terricolous spiders of South Africa will perhaps have to be 

 re-grouped and in some cases merged, the relegation of sternal 

 sigilla to a merely specific character in order to simplify matters, is 

 not sound. 



It is quite possible that sternal sigilla will afford a means of tracing 

 the generic development of such groups as the Idiopeae. As far as 

 can be seen, from out of the cross identification and synonymy of the 

 past, the fact emerges that Idiops exists in Africa and South America 

 (as well as in Central Asia, Syria, Arabia, India, and Burma) and 

 includes as synonyms the majority of species described under 

 Acauthodon. Further in this group occurs the genus Gorgyrella, 

 found only in South Africa ; Heligomerus, found in Tropical Africa, 

 India, and Ceylon, and finally Segregara, proposed for forms as pre- 

 viously defined. Now Pocock, writing on the geographical distribution 

 of the Ctenizidae (P.Z.S. 1903, pp. 351 and 357), considers that Idiops 

 reached South America, not from North America, but from Africa. 

 This and the general geographical distribution of the Idiopeae indicate 

 that Tropical Africa was the seat of origin of the group. The pro- 

 bability is that the original stock was akin to Segregara, and that the 

 latter fjeiius is a direct but numerically feeble continuation of it. From 



o 



this a branch occurred, in which muscular alteration and migration took 

 place, giving forms (c) and (D) Text-fig. 11; this form, now known 

 as Idiops, spread far and wide, and eventually reached South America, 

 whei-e it still exists, and has given rise to a specialised offshoot, 

 Pseudidiops ; in view of its success in establishing itself and its 



