i80 3 J THE BRITISH NATURALIST. 251 



pp. 370 — 371, is without doubt the species we know by that name. This 

 description is: — "Alae superiores lineares; linea alba, longitudinali, ut 

 soli margines, obscuriores, immaculata, Pedes albi." The "linea 

 alba " is most characteristic of Q tetradactyla but in the " Systema 

 Naturae," both 10th and 12th Editions (10th, p. 542, 12th, p. 900), 

 tetradactyla gets a fresh description " Alucita alis patentibus fissis 

 flavescentibus," which fits our species nowhere ; but to muddle 

 matters, the tetradactyla description of the "Fauna Suecica " is applied 

 to a new species tridactyla, and, therefore, the tridactyla of the "Systema 

 Naturae " becomes synonymous with tetradactyla of the " Fauna 

 Suecica," both representing our tetradactyla. The difficulty now 

 remains — What is the tetradactyla of the " Systema Naturae ? " The 

 " flavescentibus " is the puzzle. It might refer to the closely allied 

 baliodactyla, but this is not a Scandinavian species, and therefore very 

 improbable. It might be an entirely different species — " osteodactyla," or 

 some other — or finally, it may be that Linnaeus is practically correct, 

 and that the tetradactyla of the "Systema Naturae " is the $ of that species, 

 as the 9 is very different to the s, and is of an uniform dirty yellowish- 

 white colour. Haworth, in the " Lepidoptera Britannica," p. 477, 

 uses the Linnaean diagnosis for tetradactyla from the "Fauna Suecica," 

 and afterwards adds the description (vide above) from the same work, 

 and which, as I have before said, is most distinctly our tetradactyla. 

 But we have to remember (as also I have pointed out) that this species 

 is sexually dimorphic, that the male has dark costal and inner margins 

 with a longitudinal white line, while the female has the anterior 

 wings entirely whitish. Linnaeus may have (as I have previously 

 stated) described the sexes as distinct ; Haworth, I think, certainly 

 did. Haworth (quoting Fabricius) describes tridactyla as : — " Alucita, 

 alis fissis ; anticis bifidis albis, posticis tripartitis fuscis, Fab.," and 

 then adds : — " Parvus, distinctis alis, posticis trifidis fuscis " (" Lepi- 

 doptera Britannica," p. 477). This I consider a very fair diagnosis of 

 the female tetradactyla " (" Entomologist's Record" etc., Vol. I., p. 91). 



Imago — This pale bone-coloured species has the anterior wings 

 divided into two lobes, the apex pointed ; dusted with ochreous-grey 

 along the costa so that it is a rather duller looking insect than its 

 ally, baliodactyla ; the ochreous-grey dusting along the costa is continued 

 along the inner margin thus leaving a pale longitudinal line extending 

 throughout the central area of the wing. There is also a dark blackish 

 shade on the costa of the upper lobe. The hind-wings are divided 

 into three plumules and are of a grey colour. The hind-wings are 

 uniformly dark grey. The ground colour of the fore-wings of the 

 female is almost white throughout and without the dark shadings 

 characteristic of the males. The female has a much smaller wing 

 expanse than the male. Stainton's diagnosis is : — " 9"' — 10"'. Fore- 



