ix METHODS OF INDEXING 143
hands ; the thumb being inconvenient to print from, and having to be printed separately, even for a dabbed impression, while the fingers of either hand can be dabbed down simultaneously.
For a large collection the ten digit method is certainly the best, as it breaks up the big battalions ; also in case of one or more fingers having been injured, it gives reserve material to work upon.
We now come to the great difficulty in all classifications ; that of transitional cases. What is to be done with those prints which cannot be certainly classed as Arches, Loops, or Whorls, but which lie between some two of them? These occur about once in every forty digits, or once in every four pairs of hands. The roughest way is to put a mark by the side of the entry to indicate doubt, a better one is to make a mark that shall express the nature of the peculiarity ; thus a particular eyed pattern (Plate 10, Fig. 16, n) may be transitional between a loop'-and a whorl ; under whichever of the two it is entered, the mark might be an e to show that anyhow it is an eye. Then, when it is required to discover whether an index contains a duplicate of a given specimen in which a transitional pattern occurs, the two headings between which the doubt lies have to be searched, and the marked entries will limit the search. Many alternative ways of marking may be successfully used, but I am not yet prepared to propose one as being distinctly the best. When there are two of these marks in the same set, it
