Using the slope and y-intercept of each reference line, determine which points contain y-values less than the upper line and which points contain y-values greater than the lower line.
Create demo data. I assume you've computed the log() for each x and y since the axis scales are not log.
x = exp(linspace(2.2,5.8,500));
y = exp(log(x)+rand(size(x)).*linspace(2,.1,numel(x))-1);
h = plot(xlog, ylog, 'o');
Add reference lines. I assume you already have the slope and y-intercept info.
text(6*ones(size(yint)), slope*6+yint, compose('%d',1:numel(yint)))
Isolate dots between two reference lines. For this demo, we're isolating dots between the 3rd and 5th lines.
isBetween = ylog > slope*xlog+yint(3) & ylog < slope*xlog+yint(5);
Plot the isolated points and return their x,y values
xBetween = xlog(isBetween);
yBetween = ylog(isBetween);
h2 = plot(xBetween, yBetween, 'r.');
legend([h,h2], 'All data', 'Data between lines 3 and 5')