KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 27, N:o 3. 23 



alternately longer and shorter. — Pinn. Gästrum Ehb. Åm. III: 7 f. 23. M. Gr. V: i f. 12. Ströse 

 Klieken D. f. 1 b. N. Gastrum Donk. B. D. p. 22 Pl. III f. 10. Grun. A. D. p. 31. V. H. Syn. 

 p. 87 Pl. VIII f. 25, 27. Pant. III Pl. III f. 48. Nav. exigua Pant. III Pl. III f. 4.i (1893). 

 N. varians Gbeg. T. M. S. III p. 10 Pl. II f. 27, 28 (1855). N. Hoffmannii Pant. II p. 47 

 Pl. XIV f. 245 (1889)? 



Fresh water: Sweden! Finland! England! Ireland! Belginm (V. H.), Sea of Kära! Cape 

 DeschnefF! New Zealand! Illinois! 



Var. Jenisseyensis Grun. (1880). — Lanceolate. L. 0,038 to 0,065; B. O,oii to 0,oi7 mm. 

 Strise about 9 in 0,oi mm. more distant in the middle, where there are only a few shorter ones 

 among the longer, very finely lineate. — A. D. p. 31 Pl. I f. 28. N. Basilica [Pant. III 

 Pl. VIII f. 129 (1893)? 



Fresh or brackish water: Jenissey (Grun.), Cape Deschneff! New Zealand! New Caledonia 

 (Kinker CoU.)! 



Var. latiuscula Grun. (1880). — V. lanceolate. L. 0, 024 to 0,o6; B. 0,012 to 0,017 mm. 

 StricB 10 to 11 in 0,oi mm. The median strite not alternately longer and shorter. — A. D. p. 31. 

 Ströse Klieken D. f. 1 a. 



Fresh and slightly brackish water: Sea of Kära! Sweden (Upsala, Ronneby, Kalmar, fossil)! 

 Finland! East Cape, East Siberia! Cuxhaven (Grun.), ObexTohe and Klieken, fossil! 



Var. exigua Greg. (1854). — V. lanceolate with subrostrate or subcapitate ends. L. 0,oi7 

 to 0,03; B. 0,009 to 0,012 mm. Strise 12 to 14 in 0,oi mm — Pinnul. exigua Gbeg. M. J. p. 99 

 Pl. IV f. 14. N. Gastr. v. exigua Grun. A. D. p. 31. V. H. Syn. Pl. VIII f. 32. 



Fresh or brackish water: Gulf of Bothnia (Torneå! Piteå!) Finland, Lake Lojo, Åbo! Hun- 

 gary, fossil (Grun.), New Zealand! 



Var. horyana Pant. (1889). — V. capitate. L. 0, 04 6 to 0,0 6; B. 0,oi7 to O, o 2 mm. Strise 

 7,5 to 8,5 in 0,01 mm. radiate, coarsely punctate, puncta 17 to 18 in 0, 01 mm. Median strise 

 alternately longer and shorter. — Pant. II p. 46. 



Marine: Hungary, fossil (Pant.). 



30. N. Placentula Ehb. (1843). — V. elliptic-lanceolate, with rostrate, obtuse ends. L. 0,05 

 to 0,06; B. 0,016 to 0,028 mm. Axial area narrow, but distinct. Central area irregular, trans- 

 verse. Strise 6 to 9 in 0,oi mm., radiate throughout, coarsely lineate or punctate, shortened in 

 the middle, but not alternately longer and shorter. — Pinnul. Plac. Ehb. Am. III: 7 f. 22. M. G. 

 XII f. 19. Grun. A. D. p. 34 Pl. II f. 36. N. pusiUa Donk. B. D. p. 20 Pl. Ill f. 6 6? N. Gastrum 

 v. Plac. V. H. Syn. p. 87 Pl. VIII f. 26, 28. N. Gastrimi f. minor. Grun. F. D. Öst. Ung. XXX f. 51. 



Fresh water: Cassel »Polierschiefer» (Ehb.), Ireland Antrim Co.! Jenissey! New Zealand! 

 California! Oregon! Puerto Monte! Ecuador! 



Var, lanceolata Gbun. (1860). — V. broadly lanceolate. Ends not rostrate. L. 0,04; B. 0,oi6 

 mm. Strise 7 to 8 in 0,oi mm. — N. tumida var. lanceolata Gbun. Verh. 1860 p. 537 Pl. IV f. 44. 

 A. D. p. 34. 



Brackish water: Sea of Kära! Skienitz See near Berlin (Grun.), Neusiedlersee (Grun.). 



Nav. Placentula is very nearly akiii to Nav. Gästrum, and it is questionable whether they 

 should not be united in one species. The median strise are in Nav. Gästrum, bu.t not in Nav. Placen- 

 tula, alternately longer and shorter, but this characteristic is subject to great variation, the var. 

 Jenisseyensis having onlj»^ a few, and the var. latiuscula no, shorter median stricE. Of more im- 

 portance is it that Nav. Placentula has coarsely lineate, or almost punctate strise. Nav. anglica 

 is nearly akin to Nav. Gastrum and might be considered as a variety of it. There exists in fact 

 no limit between these three species; Nav. Placentula appears to be akin to Nav. leptostigma, 

 which has äner, distinctly punctate, strise and that to Nav. platystoma, the strise of which are 

 very finely punctate. On the other hand N. Placentttla is by its coarsely punctate strise allied 

 to the section Punctatce, among which Nav. amphibola is nearly akin to Nav. Placentula. Smaller 



