"The "Rituale Romanum" (tit. iv, cap. ii, n. I) prescribes that a clean white cloth be extended before those who receive Holy Communion. This cloth is to be of fine linen, as it is solely intended as a sort of corporal to receive the particles which may by chance fall from the hands of the priest. It is usually fastened on the sanctuary side and when in use is drawn over the top of the rail. It should extend the full length of the rail, and be about two feet wide, so that the communicant, taking it in both hands, may hold it under his chin. Its very purpose suggests that it is not to be made of lace or netting, although there is nothing to forbid its having a border of fine lace or embroidery."
We hope this bit of information is helpful to anyone who might have been unsure what to do when approaching the communion rail. And we especially thank the reader who asked the question.
Update: (04/19/2009) Although we didn't hear it, some readers have informed us that Canon Avis made it clear in pulpit announcements that hands should be placed under the linen so as to catch a dropped host if it occurred, but not as far as the chin.
(We thank St. John Cantius church in Chicago, IL for the use of the picture of the communion rail linen).