BY R. J. TILLYARD. 133 



(4) The removal of the cubital fork far distad. 



(5) The shortening and curvature of the anal veins. 



If, then, ancestors of this insect existed in Palseozoic strata, 

 we should expect them to exhibit a generalised condition in these 

 five characters. This is exactly what Sycoptproit does exhibit. 

 Without stating positively that Sycopteron lies in the ancestral 

 line of Amphienfojnum, yet we can affirm that, as far as its vena- 

 tion is concerned, the two are certainly closely allied, and 

 Sycopteron is the older type. 



Let us now examine the rest of the fossil for clues as to its 

 affinities. The first peculiarity to be noted is the huge boss-like 

 areas upon the back of the head (Text-fig. 3, c). If these be com- 

 pound eyes, then Sycopteron is certainly neither a Mecopterous 

 nor a Psocopterous insect; but, as Bolton mentions no facets on 

 these areas, we may confidently take it that they are not. They 

 must, therefore, be epicranial or occipital swellings. Now the 

 head of Sycopteron is much too prominently developed to agree 

 with the Mecopterous type. But almost all the Psocoptera have 

 a comparatively large head, with prominent development of the 

 posterior portion of the epicranium. If such a head were to be 

 crushed somewhat in becoming fossilised, its appearance would 

 certainly closely resemble that of Sycopteron. The small eyes 

 would probably be completely covered by the flattened epicranium. 



The structure of the thorax in Sycop)teron is certainly primitive, 

 and might indicate equally well affinities with several Orders, 

 including both Psocoptera and Mecoptera (Text-fig. 3, c). 



Again, in the Psocoptera, the hind wing is always small and 

 weakly chitinised. Hence, in insects of this Order which might 

 become fossilised with their w^ngs flattened down over the abdo- 

 men, no sign of the hindwing or of its venation would appear. 

 The Mecoptera, on the other hand, have, of all the insects, except 

 the Odonata and Planipennia, the most strongly chitinised hind- 

 wings, of a size almost equal to the forewings, and with a strongly 

 marked and closely similar venation. Hence, if a Mecopteron 

 became fossilised in the position we are supposing, it seems 

 inevitable that traces of the hind wings and of their main veins 

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