Keys to butterfly description terms

[Ichoker]

I've understood that much. and also that wing venation plays a major role in lepidoptera systematics. What I haven't got yet is how do you decide that the vein next to 7 is not 8 and the next not 9. what is the criteria for numbering the veins. thanks

[Silverstreak]

Perhaps Dr. Seow and Mr. Teo T.P can enlighten us ?

What I haven't got yet is how do you decide that the vein next to 7 is not 8 and the next not 9. what is the criteria for numbering the veins. thanks

[Ichoker]

anyone please?

[Psyche]

If you have Butterflies of the Malay Peninsula by Corbet & Pendlebury, then it is on page 4 & 5.

The numbering of the veins are from the lowest to the highest.

Note 3 veins are unbranched & always on the costa or forward margin, namely vein 10, 11, & 12.
(Correction: in Amathusines & some Satyrines vein 10 is joined to, ie. arises from vein 7.

Veins 7 , 8, & 9 are usually joined.
If so vein 7 is the lowest vein & vein 8 is said to arise from vein 7 & not the other way round.
likewise with vein 9.
If a vein is missing the first to be absent is assumed to be vein 8, followed by vein 9.

In the case of Delias including D. eucharis it is vein 10 , one of the unbranched costal vein which is absent, not vein 9.

The Wikipedia diagram by Bingham is a century old & outdated.
Likwwise , Sunny your diagram source is in error.

TL Seow
Clarification
The veins are arranged like the barbs of a feather.
From the central cell (= shaft or rachis of a feather) the free veins that run on one side are 12, 11, & 10 ,and on the other side 1 to 6.
At the apex 3 veins come close together & are joined to a common origin.
This is seen in most butterflies.
Sometimes vein 10 & or vein 6 also join.
In skippers all the apical veins remain free.

The Wikipedia drawing is a copy of the Delias diagram by Bingham & the veins would be considered wrongly labelled.

[Ichoker]

Thank you Dr. Seow for taking time out to answer this. That was great help. I had gathered as much from Evans' 'The Identification of Indian Butterflies, 1932', but pictures referred above confused me.