Is there a difference between 夂 and 夊? Looking at the list of Kangxi radicals over at Wikipedia, I just noticed something I haven't noticed before. Radical number 34 (夂) and 35 (夊) are virtually identical. I write these radicals in the exact same way and I've asked one native speaker who also says she writes them the same way. The example characters are 夆 and 夏.

Since I mostly use radicals to learn/teach mnemonics, I realise that the difference between these two is irrelevant. They mean (almost) the same thing and can therefore be used as one for mnemonic purposes.

However, I'm still curious about these two radicals. Is there a difference in how they are written? Is there a difference in meaning? And finally, how come that there are two very similar radicals which also has very similar meaning?
The difference between the two in writing should be clear from these drawings: http://en.wikipedia.org/wiki/Radical_35 and http://en.wikipedia.org/wiki/Radical_34 and the stroke animations from http://en.wiktionary.org/wiki/%E5%A4%8A
and http://en.wiktionary.org/wiki/%E5%A4%82

夂 is normally used at the top (for example 条條修脩务務夐) or the left (for example 处) of a character, and 夊 at the bottom (for example 愛夏复) or the right (for example 致, see http://zhongwen.com/d/173/d80.htm).

Originally both characters were quite different (see http://en.wiktionary.org/wiki/%E5%A4%8A
and http://en.wiktionary.org/wiki/%E5%A4%82), but nowadays there are typically both written as 夂 by most people and most fonts don't make the distinction anymore.