Residing as I do in HLM's home town (I once nearly bought a house on the square where he lived), I have to accord due deference to the Sage. However in his day, and still in this barbarous and illiterate age, 'ten pins' had, and has, a particular meaning in Baltimore and in a few other spots around the U.S. where the sport of duckpins is as popular, if not more popular then tenpins. 'Tenpins' is used to refer to one form of bowling as distinguished from 'duckpins'.
Believed to have been introduced by German immigrants (so HLM certainly would have known about this), duckpins is a variation on the standard tenpins game. Duckpins is played with ten pins on an alley of the same dimensions as a tenpin alley. The pins are about 2/3 as tall as tenpins and more squat in shape; hence they are more stable and more difficult to knock down. The ball used in duckpins is about the size of a large grapefruit (I forget the exact size) and has no holes, but is made of the same material as the large tenpin ball and is thus quite heavy for its size. It's held in the palm of the hand and thrown while gripped with the fingers. Lastly, in duckpins, you get to roll your ball three times in a frame if you don't score a strike on the first roll or a spare on the second.
Duckpins is much more difficult than tenpins. A perfect 300 score is almost unheard of; in fact, a score over 250 is outstanding. The size of the ball and the pins causes far fewer strikes than in tenpins and the player is often left for his second roll 2 or 3 pins which will be difficult to get down in order to achieve a spare. In fact, playing "splits" for a spare is a most important part of duckpins.
/digression
I guess HLM was only interested in the difference between tenpins and ninepins and hence didn't refer to duckpins.
