KONGL,. SV. VET. AKADEMIKNS HANDLINGAB. BAND 27, N:U 3. 23 



alternately longer and shorter. — Finn. Gastrwm Ehb. Am. Ill: 7 f. 23. M. G. V: i f. 12. Strose 

 Klieken D. f. 1 b. JST. Gastrum Done. B. D. p. 22 PI. HI f. 10. Grun. A. D. p. 31. V. H. Syn. 

 p. 87 PL Vin f. 25, 27. Pant. Ill PI. Ill f. 48. Nav. exigua Pant. Ill PI. HI f. 45 (1893). 

 N. varians Greg. T. M. S. Ill p. 10 PI. II f. 27, 28 (1855). N. Hoffmannii Pant. II p. 47 

 PI. XIV f. 245 (1889)? 



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

 Deschneff! New Zealand! Illinois! 



Var. Jenisseyensis G-run. (1880). — Lanceolate. L. 0,038 to 0,o65; 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, in 

 PL VIII f. 129 (1893)? 



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

 (Kinker CoU.)! 



Var. latiuscula Geun. (1880). — V. lanceolate. L. 0,024 to O.oe; B. 0,oi2 to 0,oi7 mm. 

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

 Strose Klieken D. f. 1 a. 



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

 Finland! East Cape, East Siberia! Cuxhaven (Grun.), Oberrohe 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,oi2 mm. Strise 12 to 14 in 0,oi mm — Pinnul. exigua Greg. 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 (Tornea! Pitea!) Finland, Lake Lojo, Abo! Hun- 

 gary, fossil (Grun.), New Zealand! 



Var. boryana Pant. (1889). — V. capitate. L. 0,04 6 to 0,o6; B. 0,oi7 to 0,02 mm. Striae 

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

 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. Striae 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. Ill: 7 f. 22. M. G. 

 XII f. 19. Grun. A. D. p. 34 PL II f. 36. N. pusilla Donk. B. D. p. 20 PL III f. 6 6? N. Gastrum 

 V. Plac. V. H. Syn. p. 87 PL VIII f. 26, 28. N. Gastrum f. minor. Grun. F. D. Ost. Ung. XXX f. 51. 



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

 California! Oregon! Puerto Monte! Ecuador! 



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

 mm. Striae 7 to 8 in 0,oi mm. — N. tumida var. lanceolata Grun. Verb. 1860 p. 537 PL IV f. 44. 

 A. D. p. 34. 



Brackish water; Sea of Kara! Skienitz See near Berlin (Grun.), Neusiedlersee (Grun.). 



Nav. Placentula is very nearly akin to Nav. Gastrum, and it is questionable whether they 

 should not be united in one species. The median striae are in Nav. Gastrum, but not in Nav. Placen- 

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

 Jenisseyensis having only a few, and the var. latiuscula no, shorter median striae. Of more im- 

 portance is it that Nav. Placentula has coarsely lineate, or almost punctate striae. 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 finer, distinctly punctate, striae and that to Nav. platy stoma, the striae of which are 

 very finely punctate. On the other hand N. Placentula is by its coarsely punctate striae allied 

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



