\psset{unit=.00625}
\pstGeonode{A}
\multido{\n=20+20}{18}{\pstGeonode[PointName=M_{\n}]%
        (\n;\n){M_\n}}
\pstGenericCurve[GenCurvFirst=A,GenCurvInc=20,
linecolor=blue,linewidth=.5\pslinewidth]{M_}{20}{360} 