160 r. T. CLEVE, SYNOPSIS OF TITE NAVICITLOID DIATOMS. 



.„ I Median striae more distaiit tlian tlie otliers 50. 



' ' \ — — not — — — C. incerta Gedn. 



j,„ ( Central area dilated to tlie ventral inai'gin C. siniiata Geeg. 



' ' \ — — not — — — C. mqualis W. Sm. 



... I Val ve almost symmetrical 52. 



ni. ' - 



I — decidely asymmetrical "iS. 



^^ \ Central area large C. Mölleriana Geun. 



' "■ I — — small C. lacMstris Ag. 



P„ J Axial area narrow 54. 



'1 — — nioderately broad 50. 



^ . I Length about 0,0 3 to 0,04 mm 55. 



■' ■ 1 — — 0,0(5 to 0,07 mm C. horealis Cl. 



^^ ( StrifB 5 in 0,oi mm C. alpina Grun. 



' ' ' \ — about 10 in 0,oi mm C. rrqiialis W. Sjt 



^„ I Axial area dilated to a small oentral area 57. 



•••5- i - - not - - - - 58. 



Stria? coarsely punctate C. Sattckii V. H. 



finely — C. Reinhardtii Grun. 



.„ J Lengtli about 0,03 mm C. leptoceros Grun. 



' \ — — 0,oG mm C. ausfriaca Grun. 



^„ ( Median ventral stri» ending in isolated puncta C. twnidtila var. .lalinormn. 



■'■ ■ t — - - not 60. 



.,, ( Terminal nodules distant fi'om the ends C. Cesatii Rabh. 



I — — approximate to — 61. 



( Median line straight, strongly exrentric 62. 



\ — — subarcuate. nearly central 03. 



P^., j Valve broad. B. 0,02 mm C. Trinvgiiliim Ehb. 



''I — narrow. B. less tlian 0,oi mm C. hebridica Gkeg. 



Central area not dilated in tlie middle C. acufmscula Cl. 



abruptly dilated into a central area 64. 



. . ) Large. L. 0,05 to 0,i mm 65. 



1 Small. L. 0,03 to 0,04 mm 66. 



,„ I Strise about 10 in 0,01 mm C. acuta A. S. 



65. -^ ,^ /-. • r. 



I — — 1/— — C. oregomca Ol. 



P„ / Central area ronnded C. lapponica Gkun. 



' \ — — dilated outwards C. stnnroveiformis Lägst. 



I 



'-{' 



„„ ( Central area 

 63. { _ _ 



1. C. inicroeepliala Grun. (1880). — V. almost sj-mmetrieal, lineai-, witli rostrate-capitate 

 ends. L. O.ok) to 0,023; B. 0,oo3 to 0, 004 mm. Median line almost central, straight; its central 

 pores approximate. Axial and central areas indistinct. Strite 24 to 30 in 0, 01 mm. almost pa- 

 rallel. — Grun. in V. H. Syn. p. 63 Pl. VIII f. 36 to 39. C. mimiscula A. S. Atl. IX f. .58 to 61? 



Fresli water: Greenland! Scotland! Sweden (Vernamo, fossil)! Belginm (V. H.), Ecnador, Banos! 



2. €. (Encyoiieiua) Cesatii Eabh. (1853). — V. nearly .symmetrical, narrow lanceolate, 

 gradually tapering from the middle to the acnte ends. L. 0,045 to 0,o.t; B. O.006 to 0, 007 mm. 

 Median line almost central, with approximate central pores and slightly cnrved terminal fissnres 

 at some distance from the ends. Axial area narrow; central area small. Striai radiate throiighout, 

 about 19 in 0, 01 mm., very finely punctate. — Aar. appendicnlata Grun. Verh. 1860 p. 552 Pl. TV 

 f. 29. Nav. Cesatii Eabh. Siissw. D. p. 39 Pl. VI f. 89. V. H. Syn. p. 88 Pl. VIII f. 35. Cym- 

 hella Cesatii Grun. A. S. Atl. LXXI f. 48, 49. 



Fresh water: Greenland! Iceland! Swedish and Russian Lappland! Scotland! Sweden ("\Ve- 

 nern)! Belgium (V. H.), Piedmont (Rabh.), Canada! 



This forni, easily recognized by the distance of its terminal nodules from the ends of tlie 

 valve, is so slightly asymmetrical, that one might regard it as a Xavicula. It seems to be an in- 

 habitant principally of northern or alpine regions. In Verh. 1860 (p. 571 Pl. VII f. 16) Grunow 

 mentions a CoUetonema chibinm as occurring together witli C. Cesatii (his Nnv. uppcndicidatn') and 



