  We report the creation of ultralong-range Sr$_2$ molecules comprising one
ground-state $5s^2$ $^1S_0$ atom and one atom in a $5sns$ $^3S_1$ Rydberg state
for $n$ ranging from 29 to 36. Molecules are created in a trapped ultracold
atomic gas using two-photon excitation near resonant with the $5s5p$ $^3P_1$
intermediate state, and their formation is detected through ground-state atom
loss from the trap. The observed molecular binding energies are fit with the
aid of first-order perturbation theory that utilizes a Fermi pseudopotential
with effective $s$-wave and $p$-wave scattering lengths to describe the
interaction between an excited Rydberg electron and a ground-state Sr atom.
