Figure 2.

Logarithmic plots (both scales logarithmic) of the size distribution of genera, assuming only background extinctions. The left-hand plot is for n₀ = 1 and the right-hand one for n₀ = 5. For both plots λ = 1. For the sake of display the points of the probability mass function have been joined by lines:- solid (μ = 1); broken (μ = 1.5) and dot-dash (μ = 0.5).