208 



HARDWICKE'S SCIENCE-GOSSIP. 



of Latreille. The species must therefore be known 

 by the first-mentioned name. 



jE. squamata, Miiller, has a priority of ninety-six 

 years over the name Ai. borealis, Zetterstedt, there- 

 fore the latter name must sink. 



Ai. juncea, Linne, stands, as also do sE. cyanea, 

 Miiller, and s£. grandis, Linne. 



The name AL. isoceles, Miiller, has a priority of 

 fifty-eight years beyond the name .<£. rufescens of Van 

 der Linden ; therefore the latter name must be 

 discarded. 



Family Agrionid.'E. 

 Sub-Family Agrionin^e. 



Agrion, Fabricius. All the species of dragon- 

 flies now known under the generic name Calopteryx 

 must be transferred here, as the species virgo was 

 Linne's type of the genus Agrion. 



Sub-Family Ccenagrionin^e. 

 Division Normostigmatina. 



Lestes, Leach This genus stands good The 

 species hitherto known as nympha must in future be 

 called dry as, Kirby, the first of the two names being 

 inadmissible on several counts. The names of the 

 other species, barbara, virens, sponsa, and viridis, 

 stand good. 



Platycnemis, Charpentier, and its species pen- 

 nipes, hold good. 



Micronympha, Kirby. This genus is usually 

 known by the synonym Isclmura, Charpentier, which 

 was, however, preoccupied. The species pumilio 

 and elegans hold good. 



Ccenagrion, Kirby. The name Agrion being 

 now in use instead of the sunk name Calopteryx, a 

 new title had to be found for those small dragon-flies 

 generally known as Agrions (cyat/iigerum excepted). 

 The British species are pulchellum, puella, and 

 mercuriale. 



Enallagma, Charpentier. This genus was erected 

 for the Agrion cyathigerum of Charpentier. 



Pyrrhosoma, Charpentier. This genus stands 

 good. The species generally called minium must 

 drop its present name in favour of nymphula, Sulzer, 

 which has a slight priority over the name given to it 

 by Harris. P. tenellum stands good. 



Erythromma, Charpentier. This genus, and also 

 its species najas, stands good. 



The general tendency of these changes is decidedly 

 for the better, as their use in this country will bring 

 our native entomologists more in touch with con- 

 tinental authors (except as regards the use of the 

 names Diplax and Calopteryx) a thing ever to be 

 desired and hitherto little attended to. We must 

 not regard even the names given in this article as 

 admitting of no further changes. Other material, of 

 which we know nothing, may occur at any time, and 

 this would, almost necessarily, upset the obtaining 



classification and nomenclature. There is, however, 

 little likehood of such a thing taking place. 



With regard to the changes in generic nomen- 

 clature, Mr. Kirby writes, "The limits of a genus 

 are always variable and its characters subject to 

 modification, both according to the increase of our 

 knowledge and to the divergent views of different 

 entomologists." The distinguished naturalist, Swain- 

 son once wrote, " Does there exist, in any class of the 

 animal kingdom, a natural group, wherein all the 

 species exhibit the whole of the typical characters? 

 Every naturalist, every systematist, knows full well 

 that no such group is to be found. It has been said 

 by one of the most distinguished naturalists that this 

 country has produced, that if a species possesses two 

 out of the three characters of the genus in which it is 

 placed, this is all we can expect ; and the reason of 

 this is obvious : if all the species possessed all such 

 characters, then there would be no gradation of 

 structure — no links in the chain of affinity — no loss 

 of one structure — and therefore no taking up of 

 another. Now, all this is diametrically opposed to 

 facts ; for the whole creation is but one connected 

 chain of such graduated progressions, unequal, 

 indeed, yet still graduated." This being so, the 

 student must rest content with a correct knowledge 

 of what is passing around him, and must go forward, 

 adopting or rejecting each new change as it occurs, 

 guided by fixed, but not entirely arbitrary, principles 

 of classification. 



SCIENCE-GOSSIP. 



Mr. Baldwin Latham recently delivered an 

 address to the Meteorological Society, in which he 

 showed that at certain seasons of the year it was 

 possible to indicate the direction and volume of the 

 flow of underground waters, even at a considerable 

 depth, from the peculiar way in which fogs lie on the 

 surface of the ground. These flows of underground 

 waters are intimately associated with underground 

 temperatures. At certain seasons of the year' there is 

 a check against the escape of the vapour arising from 

 the waters, owing to the temperature of the ground 

 acting as a condenser. In September and October 

 the vapours have a chance of escaping, hence 

 the peculiar lines of ground-fogs which mark those 

 two months. There is no question that the heavy 

 dews of September and October are largely due 

 to the condensation of the uprising underground 

 vapours. 



Professor G. V. Boys' discoveries in physics are 

 all well-known to the scientific world. Our readers 

 could not do better than procure the people's lecture 

 he delivered at the British Association under the title 

 of " Soap-bubbles," published as a half-crown volume 

 by the Society for Promoting Christian Knowledge. 



