— 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. c. 



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., striae 9 in 0,01 mm.) with unilateral 

 central area which is nearest to var. amphirhynchus (V. H. 1. c. fig. 5). 1 

 have figured it in tab. nostr., fig. 16. 



Surirella Tiirpin (1837). V. H. Traite p. 308. 



55. S. linearis W. Sar, var, constricta W. Sm.? cnfr. A. S. Atl. 

 tab. XXIII, fig. 8. 



L. 0,09 mm., B. in the middle 0,014 mm., cost* 2—3 in 0,01 mm. 

 Klong Mimse, Lem Dan. Rare. 



As the present form differs somewhat from the above fig. by A. S. 

 1 have figured it in tab. nostr., fig. 17. 



Area: the main species scattered, usually in alpine and subalpine regions: 

 var. consfrida: cum f^perie passim (de Toni Syll. p. oGS). 



56. S. angiista Ktz. ? A. S. Atl. tab. XXIII, fig. 40. 



Klong Prao, Klong Maium. 



This form agrees with the figure by A. S. which has been referred 

 by him wnth some doubt to S. angnsta. 



Area: Europe. 



57. S. siamensis Ust. nov. sp. tab. nostr., fig. 18. 



L. 0,026 mm., B. 0,oi mm., costal 4 in 0,oi mm. Valve oval, 

 costee alternant, reaching the apical axis, sti-ise 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. Ufrons Ktz. 



Hantzschia Grmi. (1877). V. H. Traite 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. Traite p. 382. 

 TryhUonella (W. Sm.) Grmi. V. H. 1. c. p. 384. 



59. N. Tryblionella Hantzsch. var. Lovidensis W. Sm. V. H. Syn. 



tab. LVII, fig. 16. 



Lem Dan (3 samples). 

 Area: Europe. 



