176 THE SCOTTISH NATURALIST 



(a) External Characters separating the Species. — In 



the female sex Sirex gigas and vS. cyaneus cannot be con- 

 founded ; the former is a dull,yellow-and-black banded insect, 

 while the latter (excluding the legs) is of a uniform metallic 

 blue-black colour. The males, on the other hand, bear con- 

 siderable superficial resemblance, both having the hind body 

 largely reddish yellow. There is, however, one character 

 by which males and females alike can be separated at a 

 glance, namely, the yellow on the temples (sides of the head 

 behind the eyes), always present in gzgas, but never in cyaneus. 

 The antennae, too, are yellow in the former and black in the 

 latter. In the females the terminal spike projecting above 

 the ovipositor is narrowly spatulate in gigcts, but sharply 

 triangular in the other. Further, a difference in the number 

 of " brachial cells " in the fore-wings — two in cyaneus as 

 against one in gigas — has been regarded as of generic 

 importance by systematists, who have consequently removed 

 cyaneus and some closely related forms to a separate genus, 

 Paururus. 



As regards the Blue-black Wood-wasps, much confusion 

 has existed in the past. For many years it was the practice 

 to record the blue-black specimens occurring in Britain under 

 the name of S.juvencus, a species diagnosed by Linnaeus in 

 1758; but in 1904 the Rev. F. D. Morice pointed out in the 

 Ent. Mo. Mag. (p. 34) that juvencus ought to have the 

 antennae widely reddish yellow towards the base, a character 

 he had not found in any specimen he had so far examined 

 from this country, all having the antennae entirely black as 

 in 6". noctilio, a form described by Fabricius in 1793. Other 

 small differences were referred to. Since then he has seen 

 from the east of England, a few specimens with the 

 characters oi \x\x& juvencus \ but so far as I can find out none 

 has as yet been recorded from Scotland. I possess, however, 

 two males from Dalmeny Park (Nov. 1899) in which the 

 antennae are partly rufescent, but they have the eighth dorsal 

 segment bluish-black all over, which is said to be a character 

 of noctilio. I am inclined to think the rufescence on the 

 antennae is due to immaturity, the more so as these two 

 specimens (which were cut out of their cells) are associated 



