The "Leapfrog" model is a "3rd" line Spear-Jackson handsaw (in 1915). 
The top  line was "Double Mermaid", 2nd line "Mermaid".  Asking price in
1915 for them in 26" skew back blade length was :
 	Double Mermaid     128/-  doz  	(Vanadium Alloy Steel)
	Mermaid	                 100/-  doz	(Silver Steel,
London Spring)
                   Leapfrog	                 70/-   
doz	(Cast Steel)
(I assume the prices are in "Shillings/Pence")   
It should be noted that in 1915 the Mermaid and Leapfrog  trademarks were
called "New Trade Marks" by Spear & Jackson.
--ErvSaws