BY R. J. TILLYARD. 131 



due only to the method of branching dichotomously, and the 

 absence of clearly-marked crossveins, — characters which are by 

 no means confined to the Mecoptera. 



I would suggest that the true costa of this insect has become 

 folded under in the fossil, and is not clearly visible. Bolton 

 says, "The costal margin seems to have been extremely delicate, 

 and to have left very faint traces of its position." This might 

 well be true of the subcosta, which is frequently a weak vein. 

 In the Mecoptera, the costa is strongly formed, but there are 

 other insects in which it is not so. This suggestion receives 

 support from the fact that, if the front vein preserved in this 

 fossil is really the costa, then Sc, R, and M all come off from a 

 common stem, in a manner that cannot be paralleled except in 

 the Homoptera, and certainly never occurs in the Mecoptera. 



Whether w^e allow that the costa was underfolded or not, the 

 following dilemma has to be faced: — 



(1) If the fossil is Mecopterous, then the naming of the veins 

 by Bolton is incorrect. The five-branched vein which he has 

 distributed between R and Rs is certainly the media; and we 

 are then driven to suppose that all the rest of the venation, 

 costad of this, has been underfolded, except a portion of Rs, which 

 would be Bolton's Sc. 



(2) If Bolton's naming of the veins is correct [or even if the 

 large extent of underfolding suggested in (1) cannot be admitted], 

 the fossil is neither Mecopterous, nor in any way related to the 

 Mecoptera, since the typical Sc, R, and Rs of that Order — the 

 latter alone of which is never less than four-branched* — are all 

 absent. 



From this dilemma, there is only one escape, viz., to admit at 

 once that the Mecopterous atiinities, much as we must regret it, 

 cannot be proved, and to seek for some more likely solution of 

 the problem. 



In Text-fig. 3, 0?, I show the venation of the forewing of the 

 very archaic insect Amphientomum paradoxum Br., from Baltic 



* Excepting in the highly reduced, recent XannochoristidiV, where it is 

 three-branched. 



