On Some South African Aviculariidae (Arachnida) 131 



trypa the ocular area is scarcely wider posteriorly than anteriorly, is 

 shorter in comparison with the width, and has the posterior row of 

 eyes smaller and more subequal in size than Pelmatorycter ; the latter 

 also has the posterior tarsi of the ? ? more heavily spined on the 

 under surface. Further, Ancylotrypa are considerably smaller and 

 slenderer in build, and the $ have shorter palps, and the $ $ more 

 oblong (or cylindrical) abdomens than in Pelmatorycter. 



Thus among Hewitt's recent additions (Ann. Transv. Mus. vol. v, 

 No. 3, p. 192, etc.) to the genus Pelmatorycter, are forms such as 

 P. parvus and P. brevipalpis, etc., which from the descriptions appear 

 to belong to Ancylotrypa ; further, a $ specimen depicted in fig. 10, 

 pi. XXVI, and referred to as a species near brevipalpis, possesses the 

 characteristic size and shape of Ancylotrypa, and would no doubt 

 possess the sternal characters also. 



Not only in Pelmatorycter and Ancylotrypa, but in the preceding 

 and other genera, sternal sigilla appear to be a sufficient generic 

 distinction. When one considers that these sigilla are the marks 

 formed bv attachments of the powerful internal thoracic muscles 

 which actuate the legs, their significance is not inconsiderable. A 



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difference iu position and size of the posterior sternal sigilla, as shown 

 by Gorgyrella and Seyregara (Text -fig. 11), can only mean a difference 

 in arrangement and action of the thoracic musculature which makes 

 the two forms entirely separate. In the above case both are ground- 

 trapdoor-tube builders, and are also alike in external appearance. 

 It is generally admitted that genera arise in evolution by branching 

 off from a common stock, and therefore intermediate forms are at 

 times only to be expected. Although the posterior sternal sigilla of 

 Gorgyrella are equivalent to the corresponding ones of Segregara, and 

 have probably been formed by the enlargement and forward migration 

 of the posterior sternal muscles of a Segregara-like stock, it seems 

 quite legitimate to consider that branch geuerically distinct. The 

 supposition of the development of Gorgyrella from a 8e</regara-\\]s.e 

 form seems borne out by the young examples of Gorgyrella, in which 

 the posterior sigilla bear more resemblance in conformation and size 

 to those of some adult forms of Segregara, whilst the adult forms do 

 not. In all specimens of Gorgyrella examined the muscle attachments 

 are as in Text-fig. 11s, and though some may perhaps be smaller and 

 slightly further apart posteriorly or vice versa, the arrangement is 

 invariably characteristic and distinct. A parallel case to this is 

 furnished by Homostola and Spiroctenus ; Hewitt considers that 

 Homostola zebrina is " an aberrant Spiroctenus standing somewhat 

 isolated in the genus owing to the large size and close approximation 



