This is a group of postcards with quite an unusual back. Those I have seen use the negatives of  the 53,000 range. i.e. 53659-53676.

Series Contents: Apparently restricted to the 53659-53676 images.

Date Published: The only dates I have are in 1907, but by analogy with the 53,000 Series I suspect they were published in 1906.

Printing: Printed by multicolour photolithography with a black halftone layer on top.

Number in Series: Unknown

Identification: The heading "Souvenir Post Card" is prominent on the back.