  The large, so-called colossal, magnetoresistivity of doped manganese oxides
based on LaMnO3 has attracted considerable attention, but only one unusual
feature of the ferromagnetic transition in these compounds. We examine in this
paper the progression of magnetic and thermodynamic behavior as the transition
temperature is made to vary from 360 K to 218 K by changing the divalent
dopant. Single crystals of La_{0.7}Sr_{0.3}MnO3, as is well known, show modest
magnetoresistivity and conventional critical behavior. La$_{0.7}$Pb$_{0.3}$
Mn$O_3$, and to an even greater extent, La$_{0.7}$Ca$_{0.3}$MnO$_3$, have
unusual magnetic properties extending more than 100 K above the transition. We
treat the properties of the latter samples in the context of a Griffiths phase
in which the transition temperature is depressed from its maximum value T_{G}
by random bond-angle bending.
