154 PROCEEDINGS OF TUE JIALACOLOGICAL SOCIETY. 



Suh-geuus Segmentina (Fleniing). 



Segmentiyia, Fleiuiug, 1817 {Planorbis nifidiis, Miill.) ; Jleinithdamus^ 

 'Leach MS.,' Tiirton, 1831 {Nautilus lacusiris, Lightf. = 

 J\ nitidus, Miill.), in synonymy ; Discus, Haldenian, 1840 

 {P. armigera^ Say), not Discus, Fitzinger, 1833 ; Plmiorhula, 

 Haldeman, 1842 {P. armigera, Say); Doitatus, 'Beck,' Gray, 

 1847 {P. armatus, Gray); Trochorhis, Benson, 1855 (P. trochoides, 

 Bens.); Ajjpendiculata, Ficinus, 1867 {P. nitidus, Miill., type 

 by inclusion) ; Ilaldemanifia, Dall, 1905 (P. JVheatleyi, Jjea). 

 Type, Planorhis nitidus, Miiller. 



Sub-genus Gyraulcs, Agassiz. 



Nautilus (sp.), Liune, 1758 [JV. crista, L.) ; Turbo (sp.), Linne, 1767 

 {T. nautilus, L. = iV. crista, L.) ; Pla?iaria, lirown, 1827 

 {PlaJiorhis alhus, Miill.), not Planaria, Miill., 1776; Gyraulus, 

 Agassiz in Charpentier, 1837 (P. hispidus, Drap. = P. albus, 

 Miill., type by later designation); Armiger, Hartmann, 1840 

 {N. crista, L.) ; Troclilea, Haldeman, 1841 (P. albus, Miill., 

 type by substitution) ; Nautilina (sp.), Stein, 1850 (iV. crista, L.) ; 

 Torquis, Dall, 1905 (P. parvus, Say). 

 Type, Planorbis albus, Miiller. 



Sub-genus Hippeutis, Agassiz. 



Ilippeutis, Agassiz, in Charpentier, 1837 {Planorbis complafintus, 

 Drap. = Helix fontana, Lightf.) ; Bathjomphalus, Agassiz, in 

 Charpentier, 1837 {H. contortxis, L.); Polygyrus, Gray, 1847 

 {H. contortxis, L.), not Poh/gi/rus, Beck, 1837; Discoidina, Stein, 

 1850 {II. contortus, L.) ; Mejietus (sp.), H. & A. Adams, 1855 

 {Planorhis operciilaris, Gould = P. dilatatus, Gld.) ; Helicorbis, 

 Benson, 1855 (P. nitidus, Gray, no7i jNIiiller = H. fontana, Lightf.) ; 

 Drepanotrema, Crosse & Fischer, 1880 (P. Yzabelensis, C. «& F.) ; 

 Heterodiscus, AVesterlund, 1902 (P. libanicus. West.), not 

 Seterodiscus, Sharp, 1886. 

 Type, Helix fontana, Lightf oot. 



Sub-genus Planorbis, s.s. Shell of moderate size, averaging 8 mm. 

 in diameter, discoidal, whorls numerous and vertically compressed, 

 sinistral, spire planulatc, umbilicus broadly dislied, margin of sjiire- 

 pit and umbilicus normally subangular, periphery carinate, aperture 

 normal, retracted above; habitat lakes and streams among aquatic 

 vegetation. 



Sub-genus Gyraulus. Shell similar to Planorbis, s.s., but smaller, 

 averaging 5 mm. in diameter, saucer-shaped, whorls moderate in 

 number and verticalh* deeper, the periphery rounded, growth 

 somewhat ultra - sinistral, spire broadly dished ; Planorbis stage 

 passed fairly early during adolescence ; habitat similar to preceding. 



Sub-genus Segmentina. Shell similar to preceding but nautiliform, 

 the whorls usually not numerous and vertically deeper, spire-pit 

 broadly funicular, umbilicus more or less depressed, aperture dentate 

 some distance back, the teeth or plaits in two series, one on the 



