zero lepton mass limit. The bounds on $q^{2}$ are given by $m^{2}_{\ell}  \leq q^{2} \leq  (m_{D}-m_{V})^{2}$ and it is seen that because of the factor $(q^{2}-m^{2}_{\ell})^{2}$ multiplying all of the helicity amplitudes, all the form factor contributions vanish at threshold $q^{2}=m^{2}_{\ell}$. This is in contrast to the case for $m_{\ell}=0$, Eq.(\[dg1\]) where the longitudinal helicity amplitude $H_{0}$ appears with a $1/q^{2}$ factor which survives at $q^{2}=0$ with a contribution proportional to a single form factor $A_{0}$. We have written the helicity amplitudes in terms of the form factors $A_{0}$, $A_{2}$ and $V$ rather than the more conventional choice [@PDG; @korner90] of $A_{1}$, $A_{2}$ and $V$. This latter choice does not connect smoothly to the massless $q^2=0$ limit and gives incorrect results for $SU(3)_F$ breaking.

To investigate the $SU(3)_{F}$ limit when the lepton mass effect is included we need to consider $q^{2}$ dependences of the form factors. For this we use the approximation $$\begin{aligned}
F(q^{2}) & \simeq & \frac{F(0)}{1-q^{2}/\Lambda^{2}_{1}+q^{4}/
\Lambda^{4}_{2}}\end{aligned}$$ where we take the values of the parameters $\Lambda_{1}$ and $\Lambda_{2}$ from [@JausF].

In Fig. \[Fig1\] we show the $q^{2}$ spectra for the ratio $[d\Gamma  (D\rightarrow \rho \mu \nu_{\mu}  )/dq^{2}]  /[d\Gamma
(D\rightarrow K^{*} \mu \nu_{\mu}  )/dq^{2}]_{m_{\mu}\neq 0}$ for different helicity contributions 