I don't consider 24 and 29 similar in shape at all- one almost a high-wing, one a mid-wing, one single tail, one double tail, 24 has almost flat sides, 29 has circular cross section. But, I suspect no one was looking at pictures anyway. More likely to me it could be a typo and just not caught. That might be easy to miss for an English major proof reader.
In fact, it seems more and more publishers are cutting back on proof reading, depending on author to proof his own work, a big mistake. This is really evident in the spelling and grammar in magazines.