344 THE entomologist's record. 



uplands, by which the insects may have voluntarily or involuntarily 

 ascended. This fact of itself would not be adequate to explain their 

 congregation at the tarn but for two further important considerations, 

 firstly, the downward rush of cold air which takes place — often with 

 boisterous force — an hour or two after sunset in all mountainous 

 districts ; secondly, the fact that, on several subsequent occasions when 

 clouds or mist for a time obscured the sun and thus interfered with 

 the general flux of temperature, strong gusts of wind sweeping across 

 the south-Avest slope of Crib-y-Ddysgwl and Clogwyn du'r Arddu, 

 were often observed to curl down over the precipice and occasionally 

 even to strike the water beneath with considerable force. Pieces of 

 paper were several times thus precipitated in the vicinity of the Llyn, 

 their gyrations in the air not only proving the strength and direction 

 of the atmos];)heric currents, but suggesting an explanation of the 

 remarkable aggregate of forms. In this connection, we may quote 

 Houzeau, as cited by Dr. Phipson in his "Researches on the History of 

 the Earth's Atmosphere," with reference to hail. He says that hail 

 is so much more frequent by day than at night, because sudden 

 currents of air (termed in French ;/rai7is or coups dc cent) are more 

 common in the daytime, and are due to the inequalities of tempera- 

 ture produced by the sun's rays falling on certain portions of the air 

 whilst other portions are in the shade. In another chapter Dr. Phipson 

 remarks, "It is now known that butterflies and other insects are 

 occasionally transported by aerial currents from the valleys to the 

 summits of the highest mountains and far out to sea." On one day 

 when a south-east wind was blowing across the shoulder of the 

 mountain and curling down as described above, large numbers of 

 Adihwnia tanaceti kept sailing in to the northern end of the tarn ; 

 these were, in all probability, brought up from the valley which runs 

 from Beddgelert to Pen-y-gwryd, swept over the slopes near the 

 summit, and precipitated by the swirling gusts into the lake. Like 

 the majority of the beetles, they had evidently been immersed for but 

 a short time. We append a complete list of the beetles collected in 

 and about this tarn, some 140 species in all. The commonest was 

 Sitones jiare.'icens, which swarmed in such thousands that our lodgings 

 were peopled for days with specimens that had settled on us and been 

 carried home. Unfortunately the landlady was under the the impres- 

 sion that we had imported a novel English form of Cimex. Single 

 examples occurred of the true Philonthiis nif/ritidtis, and of the very 

 rare Hijdnohim pnnctatas ( ? ), which Crotch records from North Wales. 

 The single specimen of PltUontlnis thennarum is unicolorous black all 

 but the elytra, which are slightly lighter. Our captures were : 



Notiophilns aqiiatirns, N. bii/uttatiis, J^'lajihrns ciipreiis, ( 'livina 

 collaris, BradyceUus niviilis, B. collaris, Harpalus ruficornis, Tapliria 

 niralis, Ajichoiiicnus alhijics, OlistJtopus rotioidatiis, Bciiihidiiun tibiale, 

 TachyviiH Jiai'ipes, Trcchiis vii)iiitt(x, Patrobiis assi)iiilis, Helophorus 

 aencipennis, Spliaeridiniii hipustiilatuvi var. inanjinatiun, Cercyon 

 obsoh'titfi, ('. hat'inorrhoidalis, Mcpasternum holctophainun , t'rijptnpleurum 

 atoiiiariiiiii, AlcorJiara laniu/inosa, Astilbus canalicidatiis, Ocytisa 

 incrassata, Hoiiialota circcllaris, H. vicina, H. tibialis, H. elotUjatula, 

 H. analis, Kncephalns coiiijdicans, TacJii/ponis chrijsomelinHs, T. 

 Jmmerosns, T. Jn/pnoriii)i, (Jilea silplwides, Tachinus riijipes, T. 

 maryincUns, T. subterrancus, Me[iacro7iiis analis, j\[i/cetoporus anf/nlan.'f 



