HARD WICKE'S S CIENCE- G OSSIP. 



20: 



whole swarms — literally thousands — of Sirex duplex 

 (Shuckard) emerged from innumerable holes, large 

 enough to admit a small pencil-case, causing great 

 terror to the occupants. As the house had been 

 built about three years (the joists of British timber), 

 there could be no doubt of the larvae having taken 

 more than that time in arriving at the perfect state." 



The larvre of the Sirices feed upon the wood of 

 fir-trees, and in Northern Europe and America are 

 sufficiently numerous to do some amount of mischief ; 



F g. 132. — Sirex juvencus (female). 



Fig. i^.—Ryssa persuasoria. 



but their numbers are kept in check by a parasitic 

 hymenopteron named Rhyssa persuasoria, the female 

 of which, with an instinct almost incredible, finds 

 out the Sirex larva; concealed and feeding in the 

 pine-wood, and through some tiny crack or crevice 

 introduces the long ovipositor, and, darting it into 

 the unfortunate caterpillar, deposits with each stab 

 an egg. The Sirices and Ephialtes afford excellent 

 examples of the two sub-orders of Securifera and 

 Peteolata into which the Hymenoptera are divided ; 

 in the former the abdomen is attached to the body 



without any contraction at the juncture, whilst in the 

 latter it is "insected " or nipped in. 



Two or three summers ago, when Sirex gigas 

 appeared in some numbers here, I obtained a speci- 

 men of Rhyssa persuasoria, which was at rest upon a 

 heap of manure, and is probably the largest specimen 

 ever taken. The dimensions given by Ratzeburg are 

 from six to ten lines long, occasionally fourteen ; but 

 my specimen even exceeds the latter measurement. 



Information respecting Sirex juvencus and its- 

 claims to be reckoned a British insect is certainly 

 desirable, and if these few notes elicit correspondence 

 upon the subject my object in writing them will be 

 attained. 



For the excellent illustrations to these notes, I am 

 indebted to my kind friend Miss Millicent Detta 

 Houghton. 



MINERALOGICAL STUDIES. 

 No. III. 



THE district of Killiney, in the county of Dublin, 

 alluded to in the last paper,* consists almost 

 exclusively of primitive rocks ; and although their 

 constituent _minerals, whether constant or accidental, 

 can hardly be said to be very numerous, they afford 

 many specimens full of interest for the student. In 

 particular, the granite vein which skirts the coast 

 from Blackrock, and suddenly terminates in Killiney 

 Bay, striking off to the south-west, contains several 

 remarkable features, especially in its felspathic 

 element. Whilst crystalline form in the felspar may 

 be considered as rare, and inferior in definition to 

 the well-formed crystals to be found in the Mourne 

 district in the county of Down (which are also remark- 

 able for their association with beryl, tourmaline, 

 topaz, &c), it is still possible to obtain masses 

 highly characteristic of this interesting mineral. I 

 have more than once picked up pieces showing very 

 fairly defined faces of 00P. 00R00. OP. Cleavage 

 faces in these forms are of course common enough, 

 with varying degrees of perfection. There are few 

 minerals in which the phenomenon of cleavage can 

 be studied more instructively than in the various 

 felspars, though the angular variations which often 

 indicate differences of species can be determined 

 only by very accurate measurements, seeing that 

 there is frequently a difference of but a few minutes 

 more or less from the 90 which distinguishes the 

 orthose or monoclinic species. The cleavage on the 

 basal section of orthoclase is very perfect, and as a 

 rule renders the mineral unmistakable, whilst that 

 on the clinopinakoid in not much inferior. There is 

 also a peculiar glassy, and sometimes nacreous ap- 

 pearance, which is present with greater or less dis- 

 tinctness in all the numerous varieties. The main 

 chemical elements are generally ascertainable with 



* No. 238, page 219. October, 1884. 



