256 38 
In some of the samples not rare. 
Varies somewhat (but with connecting forms), usually the apices are 
more capitate than figured by V.H. 1. ¢. 
Area: Europe, America, Java. 
In a, sample from Klong Prao there occurs a smaller, slightly curved 
form (L. 0,074 mm., B. 0,005 mm., strie 9 in 0,01 mm.) with unilateral 
central area which is nearest to var. amphirhynchus (V.H. l.c. fig. 5). 1 
have figured it in tab. nostr., fig. 16. 
Surirella Turpin (1827). V.H. Traité p. 368. 
55. §. linearis W. Sar. var. constricta W. Sm.? cnfr. A. S. Atl. 
tab. XXIJJ, fig. 8. 
L. 0,09 mm., B. in the middle 0,014 mm., cost 2—3 in 0,01 mm. 
Klong Munsé, Lem Dan. Rare. 
As the present form differs somewhat from the above fig. by A. 8. 
I have figured it in tab. nostr., fig. 17. 
Area: the main species scattered, usually in alpine and subalpine regions: 
var. constricta: cum specie passim (de Toni Syll. p. 568). 
56. S. angusta Kiz.? A.S. Atl. tab. XXIII, fig. 40. 
Klong Prao, Klong Majum. 
This form agrees with the figure by A. S. which has been referred 
by him with some doubt to S. angusta. 
Area: Europe. 
57. §. siamensis Ost. nov.sp. tab. nostr., fig. 18. 
L. 0,026 mm., B. 0,01 mm., coste 4 in 0,01 mm. Valve oval, 
costee alternant, reaching the apical axis, strize fine. 
Solitary in a sample from Lem Dan. 
This Surirella seems to me, in spite of its small size, to approach 
most closely to S. bifrons Ktz. 
Hantzschia Grun. (1877). V.H. Traité p. 380. 
58. H. amphioxys (Ehr.) Grun. V.H. Syn. tab. LVI, fig. 1. 
Solitary in a sample from Lem Dan. 
Area: Ubiquitous. 
Nitzschia Hassal (1845). V.H. Traité p. 382. 
Tryblionella (W.Sm.) Grun. V.H. lc. p. 384. 
59. N. Tryblionella Hantzsch. var. Lewidensis W. Sm. V. H. Syn. 
tab. LVII, fig. 16. 
Lem Dan (3 samples). 
Area: Europe. 
