Before the standardization of the point system, this name referred to a very small size of metal type, sitting between diamond and agate. At roughly 5 points, it is extremely difficult to read for extended periods and was primarily used for footnotes, pocket bibles, and directory listings where maximizing text density was more important than legibility.
Heard on the job
We'll need to set the index in pearl if we have any hope of fitting it into the last signature.