clusters is scarcer. Periods have been determined for 87 stars in NGC 3532 [$\sim 300~{\rm Myr}$; @Barnes.98b], 4 stars in Coma [$\sim 600~{\rm Myr}$; @Radick.90], 35 stars in the Hyades [$\sim 625~{\rm Myr}$; @Radick.87; @Radick.95; @Prosser.95], and 5 stars in Praesepe [$\sim 625~{\rm Myr}$; @Scholz.07].

The observations discussed above have clearly demonstrated that once a low-mass star (G and later) reaches the main sequence it begins to lose angular momentum; this is understood to be the result of a magnetized stellar wind [@Webber.67]. By comparing the rotation velocities of stars in the Pleiades and the Hyades with the Sun, @Skumanich.72 found the scaling relation $v \propto t^{-1/2}$, where $v$ is the average equatorial velocity and $t$ is the age. This can be explained by a surface angular momentum loss rate that is proportional to $\omega^3$ [@Kawaler.88] and naturally leads to a convergence in the rotation rates of stars at a given mass as seen by @Radick.87 for stars in the Hyades. The presence of solar-mass rapid rotators in the Pleiades [@VanLeeuwen.82] appears to contradict the @Skumanich.72 law and suggests that the angular momentum loss rate is saturated above some critical rotation rate $\omega_{crit}$ so that it scales as $\omega_{crit}^2\omega$ for 