46 NERITINA. 



of this form are JS\ gatKjrenosa, Schmidt, X. atrata, Ziegler, K elata, 

 Hauti"., and X. nigresoens and X.fusca, Kutschig. 



Var. CARTNATA, Kokeil. Fig. 7. 



Cingulate form : last whorl spirally constricted, with carinated 

 shoulder. 



Var. SERRATILINEA, Ziegler. Fig. 8. 



Transverse form : shell wide, with zigzag strigations, sometimes 

 almost entirely black. 



The synonyms are iV. lacustris, Olivi, N. Gardemis, Stenz, N. 

 Benacensis, Stenz, N. Mantuana, Porro, and N. atra, Parr. 



Var. CHRYsosTOMA, Kutschig. Fig. 9. 



Golden mouthed form : larger, variously strigate, aperture golden 

 yellow, posterior portion of columellar area blackish. 



N. modesta, Kiister and N. incrusfans, Ziegl., are synonyms. 



N. FLUviATiLis, Linn. PL 15, figs. 10-25. 



Shell transverse, rapidly enlarging, last whorl swollen, white, 

 light green, pink, violet, grey or brown with transversely elongated 

 or subtriangular spots of white, or darker zigzag strigations, some- 

 times irregularly banded ; aperture bluish white or yellowish, show- 

 ing the external markings by transparency, columellar margin 

 edentulous. Diam. 6-12 mill. 



Northern and Middle Europe : Great Britain., France, Holland, 

 Germany, Russia, Norway and Stveden, Italy, Dalmatia. 



This common European species is widely distrii)uted in fresh 

 Avater, its normal habitat, and occurs also in thermal and salt 

 springs, in brackish and even in sea water. Its distinguishing 

 character is its transverse form ; the colors vary considerably, but 

 the pattern is usually either transverse, nebulous light spots and 

 streaks on a dark ground, or oblique dark zigzags on alight ground, 

 the difference of appearance being due to the greater or less thick- 

 ness and frequency of the dark markings. Fig. 15 represents a 

 form from a salt stream; fig. 16 is a marine form from the Baltic 

 coasts, known as N. Baltica, Beck, and which is N. littoralis, Linn, 

 in part ; fig. 17, the N. thermalis of Boubee (V. Prevostiana, 

 Dupuy), occurs in thermal springs ; figs. 18, 19 represent specimens 

 from Southern France, described as N. Parreyssii, Villa, N Mit- 

 treana, Recluz, N. Reynesiana, Paladilhe, N. Pyrenaica, Moquin- 

 Tandoi), and V. zebrlni, Rocluz ; figs. 20, 21 ai'e from Northern 

 Italy, and have received the local names of N. rhodocolpos, Jan, N. 



