It was the Reading ticket which recieved 37.5% of the vote, and the Straight Douglas ticket which got 3.5%.
Because otherwise I'm afraid that makes no sense. 
The Australian ballot did not come into use in the USA until the late 19th century, early 20th century. An Australian ballot is one in which the government electoral officials prepare a ballot with the names of all candidates which is then given to the voter. Elections prior to that were either conducted by paper ballot or voice vote.
Originally, this amounted to a write-in ballot since a voter would write the name of a candidate on the ballot, but later the parties would prepare ballots with candidates names on the ballot which voters could then cast. This was especially convenient in the case of elections for presidential electors, where a voter could vote for many individual electors. Voters could also strike off names of individuals, or substitute their own choices.
But different elements of a party could prepare different versions of the party ballot. It appears that this is what happened in Pennsylvania, where there are no known records of votes cast for the two slates. What is shown on Dave's (and other) results, is the votes of the highest placed Breckinridge elector on the Reading slate (John Ahl), and the highest number of votes for a Douglas elector who was not on the Reading slate. The leading Democratic elector (and Douglas supporter), Joseph Laubach, had 194,834 votes vs. the 178,871 for the leading Breckinridge elector, and the 16,765 for the best non-Reading slate Douglas elector.
Candidates of the Straight Douglas slate received a few votes in almost every county, so these may have been true write-in votes, or perhaps ballots where a voter had made a manual substitution. For example, in Adams County (seat Gettysburg), the leading Breckinridge elector received 2,644 votes vs. 36 for the best non-Reading elector (48.6% vs 0.7% vs. 50.1% for Lincoln, and 0.7% for Bell).
The Straight Douglas slate was extremely concentrated. Over half the statewide vote was in Phildaelphia, where the Breckinridge elector received 28.0%, and the Straight Douglas elector received 12.0%.
The last time a State split its electors because of differences in votes cast for individual electors was 1916 in West Virginia - though of course the split in Alabama in 1960 was because the individual electors in Alabama were chosen in the Democrat primary runoff.
