Produced by the American Caramel Company of Philadelphia between 1908 and 1910, the E91 set is unnumbered and contains a total of 99 cards and can be divided into three categories by year -- E91-A, E91-B and E91-C.  For example, the McBride specimen shown below is found in the E91-C category and was thus published in 1910.  The Marquard show below was probably produced in 1909 and thus corresponds to the E91-B set.

These cards are somewhat less popular with collectors since the fronts (with a few notable exceptions, including Eddie Plank) utilize generic player images, which usually bear no resemblance to the player identified by name.