@article{JRAM_1895__115_148956,
     author = {Lothar Heffter},
     title = {Ueber gewisse {Fl\"achen} vierter {Ordnung} {(Isogonalfl\"achen).}},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {1--22},
     publisher = {mathdoc},
     volume = {115},
     year = {1895},
     zbl = {26.0744.01},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1895__115_148956/}
}